glsl-out: Add support for push constant emulation

tests/in/push-constants.param.ron

@@ -0,0 +1,9 @@
+(
+	god_mode: true,
+	glsl: (
+		version: Embedded(320),
+		writer_flags: (bits: 0),
+		binding_map: {},
+		push_constant_binding: 4,
+	),
+)

tests/in/push-constants.wgsl

@@ -0,0 +1,13 @@
+struct PushConstants {
+    multiplier: f32;
+};
+var<push_constant> pc: PushConstants;
+
+struct FragmentIn {
+    [[location(0)]] color: vec4<f32>;
+};
+
+[[stage(fragment)]]
+fn main(in: FragmentIn) -> [[location(0)]] vec4<f32> {
+    return in.color * pc.multiplier;
+}

tests/out/glsl/push-constants.main.Fragment.glsl

@@ -0,0 +1,23 @@
+#version 320 es
+
+precision highp float;
+precision highp int;
+
+struct PushConstants {
+    float multiplier;
+};
+struct FragmentIn {
+    vec4 color;
+};
+layout(std140, binding = 4) uniform PushConstants_block_0Fragment { PushConstants pc; };
+
+layout(location = 0) smooth in vec4 _vs2fs_location0;
+layout(location = 0) out vec4 _fs2p_location0;
+
+void main() {
+    FragmentIn in_ = FragmentIn(_vs2fs_location0);
+    float _e4 = pc.multiplier;
+    _fs2p_location0 = (in_.color * _e4);
+    return;
+}
+

tests/snapshots.rs

@@ -439,6 +439,7 @@ fn convert_wgsl() {
             Targets::SPIRV | Targets::METAL | Targets::HLSL | Targets::WGSL | Targets::GLSL,
         ),
         ("extra", Targets::SPIRV | Targets::METAL | Targets::WGSL),
+        ("push-constants", Targets::GLSL),
         (
             "operators",
             Targets::SPIRV | Targets::METAL | Targets::GLSL | Targets::HLSL | Targets::WGSL,