Speedup type checking using cached overload resolution results.

This change adds caches to built-in operator overload resolution and type coersion to avoid running these time-consuming operations every time.

- Adds `TypeCheckingCache` type, which is defined in check.cpp, that contains two dictionaries for the cached results of `ResolveInvoke` and `CanCoerce` calls.
- Add `destroyTypeCheckingCache` and `getTypeCheckingCache` methods to `Session` class to reuse these cached results over the entire session.

1 files changed, 3 insertions, 0 deletions

diff --git a/source/slang/syntax.h b/source/slang/syntax.h
index ebb9d814b..00f7eb95b 100644
--- a/source/slang/syntax.h
+++ b/source/slang/syntax.h
@@ -77,6 +77,9 @@ namespace Slang
         // a vector (this will be added to the cost, if any, of converting
         // the element type of the vector)
         kConversionCost_ScalarToVector = 1,
+
+        // Conversion is impossible
+        kConversionCost_Impossible = 0xFFFFFFFF,
     };
 
     // TODO(tfoley): We should ditch this enumeration