[vm/compiler] Prevent incorrect caching of mutable CompileType objects as reaching types.

In general we would like to keep previous results of type propagation passes, however this
leads to situations where CompileType objects owned by definitions are cached as reaching
types at uses that are no longer directly connected to the definition itself.

This leads to situations when type propagator updates the type of the definition in place
via Definition::UpdateType, but does not enqueue an instruction which uses this type which
leads to incorrect fix-point computation.

As a fix we make the fact that some CompileType objects are owned by definitions explicit
by assigning [CompileType::owner_] field. Whenever we encounter situation that reaching type's
owner does not match current definition flowing into use we clone compile type to disconnect
it from original owner and prevent hidden mutation.

This CL also fixes two minor issues:

- incorrect computation of non-nullable type from a nullable CompileType with a cid;
- assings CompileType to LoadIndexedUnsafe instructions emitted by prologue builder;

Fixes https://github.com/dart-lang/sdk/issues/36156

Bug: 36156
Change-Id: I6536cfe1fda033cba3524336bfbdb871b88a8b3f
Cq-Include-Trybots: luci.dart.try:vm-kernel-precomp-android-release-arm-try, vm-kernel-precomp-bare-linux-release-simarm-try, vm-kernel-precomp-bare-linux-release-simarm64-try, vm-kernel-precomp-bare-linux-release-x64-try, vm-kernel-precomp-linux-debug-x64-try, vm-kernel-precomp-linux-product-x64-try
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/98358
Commit-Queue: Vyacheslav Egorov <vegorov@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>