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>

Author: sugoi1

src/libANGLE/formatutils.cpp

@@ -138,15 +138,6 @@ 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)
 {
@@ -1080,8 +1071,8 @@ 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>, 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_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_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);