aarch64: Use VCodeConstant for f64/v128 constants (#5997)

* aarch64: Translate float and splat lowering to ISLE

I was looking into `constant_f128` and its fallback lowering into memory
and to get familiar with the code I figured it'd be good to port some
Rust logic to ISLE. This commit ports the `constant_{f128,f64,f32}`
helpers into ISLE from Rust as well as the `splat_const` helper which
ended up being closely related.

Tests reflect a number of regalloc changes that happened but also namely
one major difference is that in the lowering of `f32` a 32-bit immediate
is created now instead of a 64-bit immediate (in a GP register before
it's moved into a FP register). This semantically has no change but the
generated code is slightly different in a few minor cases.

* aarch64: Load f64/v128 constants from a pool

This commit removes the `LoadFpuConst64` and `LoadFpuConst128`
pseudo-instructions from the AArch64 backend which internally loaded a
nearby constant and then jumped over it. Constants now go through the
`VCodeConstant` infrastructure which gets placed at the end of the
function similar to how x64 works. Some minor support was added in as
well to add a new addressing mode for a `MachLabel`-relative load.

cranelift/codegen/src/prelude.isle

@@ -88,10 +88,17 @@
 
 (decl pure u32_as_u64 (u32) u64)
 (extern constructor u32_as_u64 u32_as_u64)
+(convert u32 u64 u32_as_u64)
 
 (decl pure i64_as_u64 (i64) u64)
 (extern constructor i64_as_u64 i64_as_u64)
 
+(decl u128_as_u64 (u64) u128)
+(extern extractor u128_as_u64 u128_as_u64)
+
+(decl u64_as_u32 (u32) u64)
+(extern extractor u64_as_u32 u64_as_u32)
+
 ;;;; Primitive Arithmetic ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 (decl pure u8_and (u8 u8) u8)
@@ -129,6 +136,9 @@
 (decl pure u64_xor (u64 u64) u64)
 (extern constructor u64_xor u64_xor)
 
+(decl pure u64_shl (u64 u64) u64)
+(extern constructor u64_shl u64_shl)
+
 (decl pure imm64_shl (Type Imm64 Imm64) Imm64)
 (extern constructor imm64_shl imm64_shl)
 
@@ -388,8 +398,8 @@
 (extern constructor imm64_masked imm64_masked)
 
 ;; Extract a `u64` from an `Ieee32`.
-(decl u64_from_ieee32 (u64) Ieee32)
-(extern extractor infallible u64_from_ieee32 u64_from_ieee32)
+(decl u32_from_ieee32 (u32) Ieee32)
+(extern extractor infallible u32_from_ieee32 u32_from_ieee32)
 
 ;; Extract a `u64` from an `Ieee64`.
 (decl u64_from_ieee64 (u64) Ieee64)