Support interpolation modifiers for WGSL (#5641)

* wgsl: Support interpolation modifiers

* Move struct key decorations to flattened structs.
** This includes interpolation mode decorations, which must be in the flattened struct.
* Emit interpolation attribute.
* Enable tests/render/nointerpolation.hlsl for WGSL, as a result.

This closes #5625.

* Add new expected output for 'nointerpolation' test

1 files changed, 5 insertions, 0 deletions

diff --git a/tests/render/nointerpolation.hlsl.3.expected b/tests/render/nointerpolation.hlsl.3.expected
new file mode 100644
index 000000000..4c32e2510
--- /dev/null
+++ b/tests/render/nointerpolation.hlsl.3.expected
@@ -0,0 +1,5 @@
+result code = 0
+standard error = {
+}
+standard output = {
+}