Previously, we fixed the decoding of SIMD opcodes >= 0x80 that reads an
immediate. However, we left behind a TODO for SIMD opcodes <= 0x80. This
fixes it.

Given a byte sequence such as [0xfd, 0x80, 0x80, 0x0], it decodes to the
SIMD opcode S128LoadMem (the last 3 bytes decode to 0, it is not the
most efficient encoding, but is still valid). Then, when we are decoding
the immediate memarg that follows this, we need to skip ahead 3 bytes
(opcode_length). We were not doing that previously.

This patch changes the signature of SimdLaneImmediate and
Simd8x16ShuffleImmediate to make this requirement clearer. It takes a
new argument opcode_length, which is the number of bytes the LEB encoded
opcode takes up. The pc should then be passed in unchanged.

In function-body-decoder-impl.h, we also consistently pass down
opcode_length into the various helpers, and use that value to decode
immediates.

Changes have been made to wasm-interpreter to record the opcode_length
to be passed down to helpers.

Bug: chromium:1075719
Bug: v8:10258
Change-Id: I502c9ef47d4da2abadf14218bf0da19b291ec55c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2171460Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67483}