Coerce 'case' expressions to the same type as 'condition'

Some WGSL compilers complain if e.g. case expression is signed while
condition expression is unsigned.
Insert logic to coerce the case expression to be of the same type as the condition
expression.

This addresses issue shader-slang#4921.

source/slang/slang-check-stmt.cpp

@@ -308,8 +308,11 @@ namespace Slang
         }
         else
         {
-            // TODO: need to do some basic matching to ensure the type
-            // for the `case` is consistent with the type for the `switch`...
+            // Try to coerce the case expression to the same type as the condition
+            Expr* condition = switchStmt->condition;
+            expr = coerce(CoercionSite::General, condition->type, expr);
+            // Can't think of any cases where this would fail
+            SLANG_ASSERT(expr);
         }
 
         stmt->expr = expr;