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_impl.rs

@@ -50,6 +50,7 @@ mod display {
                 Literal::Bool(v) => v.fmt(f),
                 Literal::Char(v) => write!(f, "'{}'", v.escape_debug()),
                 Literal::Int(v) => v.fmt(f),
+                Literal::Float(v) => f64::from_bits(*v).fmt(f),
                 Literal::String(v) => write!(f, "\"{}\"", v.escape_debug()),
             }
         }