[vm/compiler] Better handle small array element representations.

Moves RepresentationOfArrayElement out of LoadIndexed and StoreIndexed
into RepresentationUtils. Adjusts RepresentationOfArrayElement
to work for all concrete typed data classes. Changes
RepresentationOfArrayElement to return the precise representation of
the array element, which requires adding two new representations,
kUnboxedInt8 and kUnboxedInt16.

Remove Address::OperandSizeFor and its only (ignored) use in the
RISCV assembler and change Address::OperandSizeFor in the ARM and
ARM64 assemblers to use RepresentationUtils::OperandSize and RepresentationUtils::RepresentationOfArrayElement appropriately.

Add Boxing::NativeRepresentation, which converts representations for
unboxed integers smaller than 4 bytes to kUnboxedIntPtr and otherwise
returns the original representation. This mimics the current semantics
for LoadIndexed and StoreIndexed where returned values represented by
unboxed integer values smaller than 4 bytes are zero or sign extended
to word size appropriately, and received values represented by unboxed
integer values smaller than 4 bytes are appropriately truncated from a
word sized signed integer.

Create LoadIndexedInstr::ReturnRepresentation and
StoreIndexedInstr::ValueRepresentation, which use
Boxing::NativeRepresentation to convert the precise representation
returned by RepresentationUtils::RepresentationOfArrayElement to
the actual returned/expected representation for those instructions.
Also use Boxing::NativeRepresentation to appropriately adjust
the representations used for SIMD operations returning int8_t.

Add checks that unboxing and integer conversion never get
representations which result in a different representation when
passed to Boxing::NativeRepresentation, as those instructions do
not currently work with unboxed integer representations smaller than
4 bytes. (Adding such support can be done in a future CL.)

Inside the optimizing compiler, use the precise representation of the
array element where appropriate. That is:

* Range analysis
* Type propagation
* Redundancy elimination

This CL also cleans up how Representations are printed to C, making
that part of RepresentationUtils. It also removes the representation
printing and parsing utils from Location since they were only used by
the original IL serializer and deserializer, which has been removed.
It also renames RepresentationUtils::IsUnsigned to IsUnsignedInteger,
to make it clear that it only returns true for unboxed integer
representations.

TEST=standalone/bytedata_test

Fixes: https://github.com/dart-lang/sdk/issues/54622
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-aot-win-debug-x64-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: I8c0dab911463ee4d0c55cd59ffea9d01e0f0bb7c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/354885
Reviewed-by: Slava Egorov <vegorov@google.com>
Reviewed-by: Alexander Markov <alexmarkov@google.com>
Commit-Queue: Tess Strickland <sstrickl@google.com>