[vm/ffi] Use untagged pointer representations for FFI pointers.

Previously, the FFI used unboxed integers as a native representation
for pointers in FFI code, as the compiler only handled very specific
uses of untagged pointers flowing between instructions. Since then,
this restriction has been removed for untagged pointers that do not
point to memory managed by the GC, like FFI pointers, so now they can
have a more precise representation.

By being precise about when untagged (untagged pointers to freshly
allocated Handles and the contents of Pointer data fields) and tagged
(TypedData objects constructed to hold the byte representation of
compound data) values are expected, we can remove the need to have
untagged pointers to GC-movable objects and/or having untagged
pointers escape as unboxed integers in the generated IL.

This CL also renames kUnboxedFfiIntPtr -> kUnboxedAddress and limits
its uses specifically to where the unboxed integer represents the
numeric representation of an untagged pointer.

This CL changes CCall to take Representations for the arguments and
return value instead of what looks like an arbitrary
NativeCallingConvention. However, the serializer and deserializers for
CCall, used in IL tests, originally assumed that the argument and return
representations were kUnboxedFfiIntPtr, so providing an arbitrary
NativeCallingConvention which didn't match that assumption would cause
failures during IL tests. That assumption came from the fact that
the only creator of CCall instructions was in kernel_to_il.cc, and there
that was the case.

Now CCall builds the native calling convention during construction
and deserialization from the argument and return representations and
stores both the representations and built native calling convention
internally. In the future, if we want to create CCall instructions with
more arbitrary native calling conventions, then we'll need to handle
serialization/deserialization of arbitrary native calling conventions,
and also add consistency checks that the provided representations
appropriately match the native calling convention.

TEST=ffi vm/dart/regress_306327173_il vm/dart/address_local_pointer_il

Issue: https://github.com/dart-lang/sdk/issues/54710
Cq-Include-Trybots: luci.dart.try:vm-aot-android-release-arm64c-try,vm-aot-android-release-arm_x64-try,vm-aot-linux-debug-x64-try,vm-aot-linux-debug-x64c-try,vm-aot-mac-release-arm64-try,vm-aot-mac-release-x64-try,vm-aot-obfuscate-linux-release-x64-try,vm-aot-optimization-level-linux-release-x64-try,vm-aot-win-debug-arm64-try,vm-appjit-linux-debug-x64-try,vm-asan-linux-release-x64-try,vm-checked-mac-release-arm64-try,vm-eager-optimization-linux-release-ia32-try,vm-eager-optimization-linux-release-x64-try,vm-ffi-android-debug-arm-try,vm-ffi-android-debug-arm64c-try,vm-ffi-qemu-linux-release-arm-try,vm-ffi-qemu-linux-release-riscv64-try,vm-fuchsia-release-x64-try,vm-linux-debug-ia32-try,vm-linux-debug-x64-try,vm-linux-debug-x64c-try,vm-mac-debug-arm64-try,vm-mac-debug-x64-try,vm-msan-linux-release-x64-try,vm-reload-linux-debug-x64-try,vm-reload-rollback-linux-debug-x64-try,vm-ubsan-linux-release-x64-try,vm-win-debug-arm64-try,vm-win-debug-x64-try,vm-win-release-ia32-try
Change-Id: I34effe8fbdc80288b703e0152d5ba67ce2343400
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/353101
Reviewed-by: Daco Harkes <dacoharkes@google.com>
Commit-Queue: Tess Strickland <sstrickl@google.com>