Metal: SeparateCompoundStructDeclarations fails validation Consider GLSL: struct S { int i; } s; s=s; SeparateCompoundStructDeclarations would rewrite this to: struct S { int i; }; S s'; s=s; The interm rewrite would rewrite the specification and declaration of s, but not the use sites. The use sites would use the old type, and thus something that was not in the tree anymore. This would fail the validation. This kind of bug was previously fixed for SeparateDeclarations in commit 18fa02bebf901dd8501de3176f6052ae4ce984be. Fix by adding the logic to SeparateDeclarations, as it is already doing almost the exact task, separating `struct S { ..} a, b`. The separation is tested in GLSLTests.StructInShader and various other draw tests. These pass with MSL, but these would also fail validation if that was enabled. Bug: angleproject:375523825 Change-Id: I1697103d0ba47616dbd3159f36f9e71cb2831c4b Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5964899 Auto-Submit: Kimmo Kinnunen <kkinnunen@apple.com> Commit-Queue: Kimmo Kinnunen <kkinnunen@apple.com> Reviewed-by: Geoff Lang <geofflang@chromium.org>