[llvm] [nfc][InstrProf]Simplify instrumentation profile reader and writer code (PR #93346)

[Kazu Hirata via llvm-commits]

kazutakahirata wrote:

Thank you for cleaning up these things!  I like where things are going overall.  Now, would you mind creating focused patches that do one thing.

- I think the `GET_VERSION` clean up should call a method in `Header`.  If `Header->getVersion()` is confusing, you might say `Header->getIndexedProfileVersion()` or something.  I wouldn't save the version in `ProfileVersion`.  Instead, I would keep calling `Header->getIndexedProfileVersion()`.
- `read_and_decrement` should be named `readAndDecrment` or `readAndDecrement` according to the LLVM Coding Standards.  Now, I feel a bit uneasy about going backward.  Let's discuss this in a separate patch.

https://github.com/llvm/llvm-project/pull/93346