In the latest wasm-gc spec, rtts of abstract types are no longer
allowed. Consequently, canonical rtts of concrete types always have
a depth of 0.

Changes:
- Change the immediate argument of rtts to a type index over a heap
  type. Abstract it with TypeIndexImmediate in function body decoding.
  This affects:
  value_type.h, read_value_type(), decoding of relevant opcodes,
  wasm subtyping, WasmInitExpr, consume_init_expr(), and
  wasm-module-builder.cc.
- In function-body-decoder-impl.h, update rtt.canon to always produce
  an rtt of depth 0.
- Pass a unit32_t type index over a HeapType to all rtt-related
  utilities.
- Remove infrastructure for abstract-type rtts from the wasm compilers,
  setup-heap-internal.cc, roots.h, and module-instantiate.cc.
- Remove ObjectReferenceKnowledge::rtt_is_i31. Remove related branches
  from ref.test, ref.cast and br_on_cast implementations in the wasm
  compilers.
- Remove unused 'parent' field from WasmTypeInfo.
- Make the parent argument optional in NewWasmTypeInfo, CreateStructMap,
  and CreateArrayMap.
- Use more convenient arguments in IsHeapSubtypeOf.
- Update tests.

Bug: v8:7748
Change-Id: Ib45efe0741e6558c9b291fc8b4a75ae303146bdc
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2642248
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72321}