This commit is the continuation of bytecodealliance#10943 for component instances. The
allocation/vmctx infrastructure was additionally refactored to be shared for
both core and component instances since they behave the exact same way anyway.
This further enables sharing various methods like `vmctx_plus_offset` which are
pretty unsafe internally.

Like bytecodealliance#10943 this necessitated removal of `Index` implementations because
`IndexMut` is not compatible with the returned type being `Pin<&mut T>`
so they were replaced by inherent `get` and `get_mut` methods on the
component instance id type.

Closes bytecodealliance#10933

This commit is the continuation of #10943 for component instances. The
allocation/vmctx infrastructure was additionally refactored to be shared for
both core and component instances since they behave the exact same way anyway.
This further enables sharing various methods like `vmctx_plus_offset` which are
pretty unsafe internally.

Like #10943 this necessitated removal of `Index` implementations because
`IndexMut` is not compatible with the returned type being `Pin<&mut T>`
so they were replaced by inherent `get` and `get_mut` methods on the
component instance id type.

Closes #10933

This commit fixes another issue we've discovered in the wasip3
prototyping repository about a code pattern in wasm which Miri flags as
un-sound. Specifically what happened was:

* Invocation of WebAssembly went through `VMFuncRef::array_call` which
  takes a `&self` parameter.

* Inside of WebAssembly though a `ref.func` instruction, or anything
  else that references the original exported function, will
  re-initialize the `VMFuncRef` which writes the `&self` up the stack,
  which is not sound.

Fixing this required changing the signature of `array_call` from `&self`
to `me: NonNull<VMFuncRef>`, and the signature was already `unsafe` so
this is a new unsafe contract for that signature.

In fixing this, however, it was discovered that a mistake was made
in bytecodealliance#10943 where some internal functions for re-initializing a
`VMFuncRef` relied on the previous signature of `&mut self` but that PR
switche to `&self`. This PR corrects these signatures to `Pin<&mut Self>`
and then plumbs around the necessary changes, notably causing some
refactoring in component-related bits.

This commit fixes another issue we've discovered in the wasip3
prototyping repository about a code pattern in wasm which Miri flags as
un-sound. Specifically what happened was:

* Invocation of WebAssembly went through `VMFuncRef::array_call` which
  takes a `&self` parameter.

* Inside of WebAssembly though a `ref.func` instruction, or anything
  else that references the original exported function, will
  re-initialize the `VMFuncRef` which writes the `&self` up the stack,
  which is not sound.

Fixing this required changing the signature of `array_call` from `&self`
to `me: NonNull<VMFuncRef>`, and the signature was already `unsafe` so
this is a new unsafe contract for that signature.

In fixing this, however, it was discovered that a mistake was made
in #10943 where some internal functions for re-initializing a
`VMFuncRef` relied on the previous signature of `&mut self` but that PR
switche to `&self`. This PR corrects these signatures to `Pin<&mut Self>`
and then plumbs around the necessary changes, notably causing some
refactoring in component-related bits.