cl-ast: Add float support

- Smuggle floats as integers to maintain `eq`
- This is bad, but not terrible for spec-compliant floats. Might have issues with NaN.

cl_parser: Smuggle floats

cl_interpret: unpack smuggled floats in float literal node

compiler/cl-ast/src/ast.rs

@@ -36,6 +36,7 @@ pub enum Literal {
     Bool(bool),
     Char(char),
     Int(u128),
+    Float(u64),
     String(String),
 }