Convert scalar_to_vector to ISLE (AArch64) (#4401)

* Convert `scalar_to_vector` to ISLE (AArch64)

Converted the exisiting implementation of `scalar_to_vector` for AArch64 to
ISLE.

Copyright (c) 2022 Arm Limited

* Add support for floats and fix FpuExtend

- Added rules to cover `f32 -> f32x4` and `f64 -> f64x2` for
`scalar_to_vector`
- Added tests for `scalar_to_vector` on floats.
- Corrected an invalid instruction emitted by `FpuExtend` on 64-bit
values.

Copyright (c) 2022 Arm Limited

cranelift/codegen/src/machinst/isle.rs

@@ -299,6 +299,14 @@ macro_rules! isle_prelude_methods {
             }
         }
 
+        #[inline]
+        fn int_bool_fits_in_32(&mut self, ty: Type) -> Option<Type> {
+            match ty {
+                I8 | I16 | I32 | B8 | B16 | B32 => Some(ty),
+                _ => None,
+            }
+        }
+
         #[inline]
         fn ty_int_bool_64(&mut self, ty: Type) -> Option<Type> {
             match ty {