The COPY inserted for liverange split during sgpr-regalloc
pipeline currently breaks the BB prolog during the subsequent
vgpr-regalloc phase while spilling and/or splitting the vector
liveranges. This patch fixes it by correctly including the
the LR split instructions during sgpr-regalloc and wwm-regalloc
pipelines into the BB prolog.

For some targets, it is required to identify the COPY instruction
corresponds to the RA inserted live range split. Adding the new
flag `MachineInstr::LRSplit` to serve the purpose.

Fix subcommand detection when subcommand used with positional arguments.
When there is only one valid subcommand passed,
`ArgList::getSubCommand()` should return the correct subcommand even
there are other positionals passed.

Optimize the FactManager and DataflowAnalysis classes by using vector-based storage with ID-based lookups instead of maps.

- Added a `FactID` type using the `utils::ID` template to uniquely identify facts
- Modified `Fact` class to store and manage IDs
- Changed `FactManager` to use vector-based storage indexed by block ID instead of a map
- Updated `DataflowAnalysis` to use vector-based storage for states instead of maps
- Modified lookups to use ID-based indexing for better performance

Improves compile time hit on long-tail targets like `tools/clang/lib/CodeGen/CMakeFiles/obj.clangCodeGen.dir/TargetBuiltins/RISCV.cpp.o`​ from [21%](http://llvm-compile-time-tracker.com/compare_clang.php?from=6e25a04027ca786b7919657c7df330a33985ceea&to=20b42efa277c8b1915db757863e1fc26531cfd53&stat=instructions%3Au&sortBy=absolute-difference) to [3.2%](http://llvm-compile-time-tracker.com/compare_clang.php?from=6e25a04027ca786b7919657c7df330a33985ceea&to=d2d1cd1109c3a85344457bfff6f092ae7b96b211&stat=instructions%3Au&sortBy=absolute-difference)

This is needed to allow using these APIs with callable objects that
transitively capture move-only constructs. These come up very widely
when writing concurrent code such a `std::future`, `std::promise`,
`std::unique_lock`, etc.

This patch fixes:

  clang/lib/CodeGen/CGBuiltin.cpp:1216:13: error: unused variable
  'CAT' [-Werror,-Wunused-variable]

This is to allow us to test rematting i64 lds in #166774. Checked and
we're still rematting the same lis on rv64 in this test.

This PR fixes #157637 by printing ANSI sequence "\r\x1b[K" to empty the
line before calling to `el_wgets`. Later when `el_wgets` prints the real
prompt, all wrongly printed characters are removed from the terminal.

zstd usually offers better compression ratios, but also offers much
higher decompression speeds, which can tangibly impact image unpack
times. Enable this by default given it is a two line change that is
transparent at image pull time given most container runtimes these days
supported zstd compressed images.