Changes:
- Add struct.new_with_rtt as a new WasmInitExpr. Parse it in
  consume_init_expr(). Add it to
  InstanceBuilder::EvaluateInitExpression().
- Change WasmInitExpr::operand_ to vector operands_.
- In consume_init_expr(), use parsed over hard-coded opcode length.
- Improve WasmStruct::WasmStructPrint slightly.
- Add Factory::NewWasmStruct().
- Add WasmValue::CopyToWithSystemEndianness.
- In wasm-module-builder.js, generalize emit_init_expr for expressions
  with operands. Add missing init. expression types.
- Add tests.

Bug: v8:7748
Change-Id: Ica12378d202730aff1b57c7d4240aa00ef124f8e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2940893
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75006}