Implement spec const for generic parameter (#7121)

Close #6840.

This PR add supports to use specialize constant in generic parameter, and that parameter can also be used as array size, e.g. following code should work:

```
struct MyStruct<let N: int> { float buffer[N]; }
MyStruct<SpecConstVar> s;
```

- Loose the restriction from Link-Time to SpecializationConstant when extract generic argument
- Tweak the logic of how we decide whether a inst is hoistable. Besides checking existing hoistable flag of each 
  IRInst, when we detect a IRInst's type is SpecConstRateType, we will treat that inst hoistable. Because IRInst in 
  global scope can be deduplicated, and every SpecConstRateType inst should be in the global scope or IRGeneric 
  scope (which will be at global scope after specialization).
- Remove the SpecConstIntVal to IRInst map in IR lowering logic, because we already have way to deduplicate the 
  global scope IR.

1 files changed, 3 insertions, 0 deletions

diff --git a/source/slang/slang-ir-clone.cpp b/source/slang/slang-ir-clone.cpp
index 5bb1c1210..1a020ec26 100644
--- a/source/slang/slang-ir-clone.cpp
+++ b/source/slang/slang-ir-clone.cpp
@@ -93,6 +93,9 @@ IRInst* cloneInstAndOperands(IRCloneEnv* env, IRBuilder* builder, IRInst* oldIns
         auto newOperand = findCloneForOperand(env, oldOperand);
 
         newOperands[ii] = newOperand;
+
+        if (isArithmeticInst(oldInst))
+            newType = maybeAddRateType(builder, newOperand->getFullType(), newType);
     }
 
     // Finally we create the inst with the updated operands.