[nfc][llvm-profdata] Use cl::Subcommand to organize subcommand and options in llvm-profdata (#71328)

- The motivation is to reduce the number of arguments passed around
(e.g., from `show_main` to `show*Profile`). In order to do this, move
function-defined options to global variables, and create
`cl::SubCommand` for {show, merge, overlap, order} to organize options.
- The side-effect by extracting function local options to a C++
namespace is that the extracted options are no longer (lazily)
initialized when the enclosing function runs for the first time.
- `cl::Subcommand` support (introduced in
https://lists.llvm.org/pipermail/llvm-dev/2016-June/101804.html) could
put options in a per-subcommand namespace.
- One option could belong to multiple subcommand. This patch defines
most of the options once and associates them with multiple subcommands
except
1. `overlap` and `show` both has `value-cutoff` with different default
values
([former](https://github.com/llvm/llvm-project/blob/64f62de96609dc3ea9a8a914a9e9445b7f4d625d/llvm/tools/llvm-profdata/llvm-profdata.cpp#L2352)
vs
[latter](https://github.com/llvm/llvm-project/blob/64f62de96609dc3ea9a8a914a9e9445b7f4d625d/llvm/tools/llvm-profdata/llvm-profdata.cpp#L3009)).
Define 'OverlapValueCutoff' and 'ShowValueCutoff' respectively.
2. `show` supports three profile formats in `ProfileKind` while
{`merge`, `overlap`} supports two. Define separate options.
- Clean up obsolete code as a result, including `-h` and `--version`
customizations. These two options are supported for all commands.
Results pasted.
- [-h and
--help](https://gist.github.com/minglotus-6/387490e5eeda2dd2f9c440a424d6f360)
output.
-
[--version](https://gist.github.com/minglotus-6/f905abcc3a346957bd797f2f84c18c1b)
- [llvm-profdata show
--help](https://gist.github.com/minglotus-6/f143079f02af243a94758138c0af471a)

This PR should be `llvm-profdata` only. It depends on
#71981

Author: mingmingl-llvm

llvm/test/tools/llvm-profdata/errors.test

@@ -5,4 +5,4 @@ RUN: not llvm-profdata show file -o file 2>&1 | FileCheck %s --check-prefix SHOW
 SHOW-OUT: Input file name cannot be the same as the output file name!
 
 RUN: not llvm-profdata 2>&1 | FileCheck %s --check-prefix EMPTY
-EMPTY: No command specified!
+EMPTY: No subcommand specified!

llvm/test/tools/llvm-profdata/version.test

@@ -1,4 +1,3 @@
 # RUN: llvm-profdata --version | FileCheck %s
 
-# CHECK: llvm-profdata
 # CHECK: LLVM version {{.*}}