Revert "Allow rendering to half float in ES2 contexts when possible"

This reverts commit 1dc0d39.

Reason for revert: Causes a failure on the bots. See: http://anglebug.com/5206

Original change's description:
> Allow rendering to half float in ES2 contexts when possible
>
> According to the EXT_color_buffer_half_float spec:
>
> "Dependencies on OES_texture_half_float
>
>     If OES_texture_half_float is not supported, then all references to
>     RGBA16F_EXT, RGB16F_EXT, RG16F_EXT, R16F_EXT, HALF_FLOAT_OES and
>     half should be ignored.
>
>     If OES_texture_half_float is supported, textures created with:
>
>         <internalformat> = RGBA
>         <format> = RGBA
>         <type> = HALF_FLOAT_OES
>
>     are renderable."
>
> This fixes 4 viz_unittests when running with SwANGLE:
>     All/GLI420ConverterPixelTest.ScaleAndConvert/0
>     All/GLI420ConverterPixelTest.ScaleAndConvert/1
>     GLScalerPixelTest.Example_ScaleAndExportForScreenVideoCapture
>     GLScalerPixelTest.ScalesWithColorManagement
>
> Bug: angleproject:5174
> Change-Id: If8623b1edbc8f0bac83513ea202ef49ad388101c
> Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2489726
> Commit-Queue: Alexis Hétu <sugoi@chromium.org>
> Reviewed-by: Geoff Lang <geofflang@chromium.org>

TBR=sugoi@chromium.org,geofflang@chromium.org,sugoi@google.com

Change-Id: Iab2df8ac563661fcf270425408b17e7bbe48a255
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: angleproject:5174
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2490820
Reviewed-by: Alexis Hétu <sugoi@chromium.org>
Commit-Queue: Alexis Hétu <sugoi@chromium.org>

Author: Alexis Hétu

src/libANGLE/formatutils.cpp

@@ -138,6 +138,15 @@ static bool RequireExtOrExtOrExt(const Version &, const Extensions &extensions)
     return extensions.*bool1 || extensions.*bool2 || extensions.*bool3;
 }
 
+static bool UnsizedHalfFloatOESRGBATextureAttachmentSupport(const Version &clientVersion,
+                                                            const Extensions &extensions)
+{
+    // dEQP requires ES3 + EXT_color_buffer_half_float for rendering to RGB[A] + HALF_FLOAT_OES
+    // textures but WebGL allows it with just ES 2.0
+    return (clientVersion.major >= 3 || extensions.webglCompatibility) &&
+           extensions.colorBufferHalfFloat;
+}
+
 // R8, RG8
 static bool SizedRGSupport(const Version &clientVersion, const Extensions &extensions)
 {
@@ -1071,8 +1080,8 @@ static InternalFormatInfoMap BuildInternalFormatInfoMap()
     AddRGBAFormat(&map, GL_RGBA,         false, 16, 16, 16, 16, 0, GL_RGBA, GL_HALF_FLOAT,                   GL_FLOAT, false, NeverSupported,                                                             NeverSupported,                                  NeverSupported,                                  NeverSupported, NeverSupported);
     AddRGBAFormat(&map, GL_RED,          false, 16,  0,  0,  0, 0, GL_RED,  GL_HALF_FLOAT_OES,               GL_FLOAT, false, RequireExtAndExt<&Extensions::textureHalfFloat, &Extensions::textureRG>,    RequireExt<&Extensions::textureHalfFloatLinear>, AlwaysSupported,                                 NeverSupported, NeverSupported);
     AddRGBAFormat(&map, GL_RG,           false, 16, 16,  0,  0, 0, GL_RG,   GL_HALF_FLOAT_OES,               GL_FLOAT, false, RequireExtAndExt<&Extensions::textureHalfFloat, &Extensions::textureRG>,    RequireExt<&Extensions::textureHalfFloatLinear>, AlwaysSupported,                                 NeverSupported, NeverSupported);
-    AddRGBAFormat(&map, GL_RGB,          false, 16, 16, 16,  0, 0, GL_RGB,  GL_HALF_FLOAT_OES,               GL_FLOAT, false, RequireExt<&Extensions::textureHalfFloat>,                                  RequireExt<&Extensions::textureHalfFloatLinear>, RequireExt<&Extensions::colorBufferHalfFloat>, NeverSupported, NeverSupported);
-    AddRGBAFormat(&map, GL_RGBA,         false, 16, 16, 16, 16, 0, GL_RGBA, GL_HALF_FLOAT_OES,               GL_FLOAT, false, RequireExt<&Extensions::textureHalfFloat>,                                  RequireExt<&Extensions::textureHalfFloatLinear>, RequireExt<&Extensions::colorBufferHalfFloat>, NeverSupported, NeverSupported);
+    AddRGBAFormat(&map, GL_RGB,          false, 16, 16, 16,  0, 0, GL_RGB,  GL_HALF_FLOAT_OES,               GL_FLOAT, false, RequireExt<&Extensions::textureHalfFloat>,                                  RequireExt<&Extensions::textureHalfFloatLinear>, UnsizedHalfFloatOESRGBATextureAttachmentSupport, NeverSupported, NeverSupported);
+    AddRGBAFormat(&map, GL_RGBA,         false, 16, 16, 16, 16, 0, GL_RGBA, GL_HALF_FLOAT_OES,               GL_FLOAT, false, RequireExt<&Extensions::textureHalfFloat>,                                  RequireExt<&Extensions::textureHalfFloatLinear>, UnsizedHalfFloatOESRGBATextureAttachmentSupport, NeverSupported, NeverSupported);
     AddRGBAFormat(&map, GL_RED,          false, 32,  0,  0,  0, 0, GL_RED,  GL_FLOAT,                        GL_FLOAT, false, RequireExtAndExt<&Extensions::textureFloatOES, &Extensions::textureRG>,     RequireExt<&Extensions::textureFloatLinearOES>,  AlwaysSupported,                                 NeverSupported, NeverSupported);
     AddRGBAFormat(&map, GL_RG,           false, 32, 32,  0,  0, 0, GL_RG,   GL_FLOAT,                        GL_FLOAT, false, RequireExtAndExt<&Extensions::textureFloatOES, &Extensions::textureRG>,     RequireExt<&Extensions::textureFloatLinearOES>,  AlwaysSupported,                                 NeverSupported, NeverSupported);
     AddRGBAFormat(&map, GL_RGB,          false, 32, 32, 32,  0, 0, GL_RGB,  GL_FLOAT,                        GL_FLOAT, false, RequireExt<&Extensions::textureFloatOES>,                                   RequireExt<&Extensions::textureFloatLinearOES>,  NeverSupported,                                  NeverSupported, NeverSupported);