[wasm] Improve SIMD vector equality operator (#79719)

[wasm] Improve SIMD vector equality operator (#79719)

Improve the code we emit for vector equality. Instead of using multiple shuffles, use alltrue instructions

    i8x16.all_true(a: v128) -> i32
    i16x8.all_true(a: v128) -> i32
    i32x4.all_true(a: v128) -> i32
    i64x2.all_true(a: v128) -> i32

That saves size and greatly improves performance. For example Span's SequenceEqual improves like this on chrome.

| measurement | old | new |
|-:|-:|-:|
|              Span, SequenceEqual bytes |     0.0087ms |     0.0021ms |
|              Span, SequenceEqual chars |     0.0174ms |     0.0042ms |

The dotnet.wasm size drops by cca 20kbytes for bench sample.

The code diff:

```
> wa-diff -d -f corlib_System_SpanHelpers_SequenceEqual_byte__byte__uintptr dotnet.old.wasm dotnet.new.wasm
...
          v128.load    [SIMD]
          i8x16.eq    [SIMD]
-         local.tee $4
+         i8x16.all.true    [SIMD]
-         local.get $4
-         i8x16.shuffle 0x00000000000000000f0e0d0c0b0a0908    [SIMD]
-         local.get $4
-         v128.and    [SIMD]
-         local.tee $4
-         local.get $4
-         i8x16.shuffle 0x00000000000000000000000007060504    [SIMD]
-         local.get $4
-         v128.and    [SIMD]
-         local.tee $4
-         local.get $4
-         i8x16.shuffle 0x00000000000000000000000000000302    [SIMD]
-         local.get $4
-         v128.and    [SIMD]
-         local.tee $4
-         local.get $4
-         i8x16.shuffle 0x00000000000000000000000000000001    [SIMD]
-         local.get $4
-         v128.and    [SIMD]
-         i8x16.extract.lane.u 0    [SIMD]
          i32.eqz
          if
...
```