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/isa/aarch64/inst/emit.rs

@@ -1688,7 +1688,7 @@ impl MachInstEmit for Inst {
                 let rd = allocs.next_writable(rd);
                 let rn = allocs.next(rn);
                 sink.put4(enc_fpurr(
-                    0b000_11110_00_1_000000_10000 | (size.ftype() << 13),
+                    0b000_11110_00_1_000000_10000 | (size.ftype() << 12),
                     rd,
                     rn,
                 ));