Legalize the Entry-point for WGSL (#5498)

* Legalize the Entry-point for WGSL

The return type of the entry-point needs to be legalized when targeting
WGSL.
This commit flattens the nested-structs of the return type and the input
parameters of the entry-point.

Most of code is copied from the legalization code for Metal. The
following functions are exactly same to the implementation for Metal or
almost same.
- flattenInputParameters() : 136 lines
- reportUnsupportedSystemAttribute() : 7 lines
- ensureResultStructHasUserSemantic() : 46 lines
- struct MapStructToFlatStruct : 176 lines
- flattenNestedStructs() : 95 lines
- maybeFlattenNestedStructs() : 42 lines
- _replaceAllReturnInst() : 19 lines
- _returnNonOverlappingAttributeIndex() : 16 lines
- _replaceAttributeOfLayout() : 23 lines
- tryConvertValue() : 41 lines
- legalizeSystemValueParameters() : 11 lines

They need to be refactored to reduce the duplication later.

The test case, `tests/compute/assoctype-lookup.slang`, had a bug that
the compute shader was trying to use the varying input/output with the
user defined semantics.

This commit removes the user defined semantics, because the compute
shaders cannot use the user defined semantics.

---------

Co-authored-by: slangbot <186143334+slangbot@users.noreply.github.com>

1 files changed, 3 insertions, 3 deletions

diff --git a/tests/compute/assoctype-lookup.slang b/tests/compute/assoctype-lookup.slang
index 348391e21..8a032528b 100644
--- a/tests/compute/assoctype-lookup.slang
+++ b/tests/compute/assoctype-lookup.slang
@@ -16,8 +16,8 @@ struct StandardBoneWeightSet : IBoneWeightSet
 {

     struct PackedType

     {

-        uint boneIds : BONEIDS;

-        uint boneWeights : BONEWEIGHTS;

+        uint boneIds;

+        uint boneWeights;

     };

     PackedType field;

 };

@@ -55,4 +55,4 @@ void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
     int inputVal = int(tid);

     int outputVal = test(inputVal);

     gOutputBuffer[tid] = outputVal;

-}
\ No newline at end of file
+}