Changes made to the Wasm module builder:
- Create emit_u64v for emitting a LEB128 that conceptually represent
an 64-bits integer.
- Differentiate toBuffer and toUint8Array for returning respectively
ArrayBuffer and a Uint8Array.
- Moved wasmF32Const and wasmF64Const functions because we can take
advantage of the existing cached conversion buffers. Also, declaring
them in the constants file will collide with the module-builder since
they are loaded in the same scope.
- The byte_view buffer (used by some conversions to bytes) switched from
Int8Array to Uint8Array.

Changes made to the Wasm contants:
- Add a new kSharedHasMaximumFlag flag for shared memory with a maximum
value.

Bug: v8:8726
Change-Id: If16c59896cfa1d42008da413e2e144b73a0fa5ce
Reviewed-on: https://chromium-review.googlesource.com/c/1443062Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Sven Sauleau <ssauleau@igalia.com>
Cr-Commit-Position: refs/heads/master@{#59213}