getBufferEnd() already returns const char *.

Factor out code in `populateCounters()` and `populateCoverage()` used to
grab the record into `PGOUseFunc::getRecord()` to reduce code
duplication. And return `NamedInstrProfRecord` in `getInstrProfRecord()`
to avoid an unnecessary cast. No functional change is intented.

Re-apply https://github.com/llvm/llvm-project/pull/139997 after fixing the use-of-uninitialized-memory error
(https://lab.llvm.org/buildbot/#/builders/94/builds/7373).

Tested: The error is reproduced with
https://github.com/llvm/llvm-zorg/blob/main/zorg/buildbot/builders/sanitizers/buildbot_bootstrap_msan.sh
without the fix, and test pass with the fix.


**Original commit message:**

https://github.com/llvm/llvm-project/pull/138170 introduces classes to
operate on data access profiles. This change supports the read and write
of `DataAccessProfData` in indexed format of MemProf (v4) as well as its
the text (yaml) format.

For indexed format:
* InstrProfWriter owns (by `std::unique_ptr<DataAccessProfData>`) the
data access profiles, and gives a non-owned copy when it calls
`writeMemProf`.
* MemProf v4 header has a new `uint64_t` to record the byte offset of
data access profiles. This `uint64_t` field is zero if data access
profile is not set (nullptr).
* MemProfReader reads the offset from v4 header and de-serializes
in-memory bytes into class `DataAccessProfData`.

For textual format:
* MemProfYAML.h adds the mapping for DAP class, and make DAP optional
for both read and write.

099a0fa (by @snehasish) introduces v4 which contains CalleeGuids in
CallSiteInfo, and this change changes the v4 format in place with data
access profiles. The current plan is to bump the version and enable v4
profiles with both features, assuming waiting for this change won't
delay the callsite change too long.

---------

Co-authored-by: Kazu Hirata <kazu@google.com>

Reverts llvm/llvm-project#139997

Sanitizer failures
(https://lab.llvm.org/buildbot/#/builders/94/builds/7373)

Will fix forward later.

https://github.com/llvm/llvm-project/pull/138170 introduces classes to
operate on data access profiles. This change supports the read and write
of `DataAccessProfData` in indexed format of MemProf (v4) as well as its
the text (yaml) format.

For indexed format:
* InstrProfWriter owns (by `std::unique_ptr<DataAccessProfData>`) the
data access profiles, and gives a non-owned copy when it calls
`writeMemProf`.
* MemProf v4 header has a new `uint64_t` to record the byte offset of
data access profiles. This `uint64_t` field is zero if data access
profile is not set (nullptr).
* MemProfReader reads the offset from v4 header and de-serializes
in-memory bytes into class `DataAccessProfData`.

For textual format:
* MemProfYAML.h adds the mapping for DAP class, and make DAP optional
for both read and write.

099a0fa (by @snehasish) introduces v4 which contains CalleeGuids in
CallSiteInfo, and this change changes the v4 format in place with data
access profiles. The current plan is to bump the version and enable v4
profiles with both features, assuming waiting for this change won't
delay the callsite change too long.

---------

Co-authored-by: Kazu Hirata <kazu@google.com>

Part of a larger refactoring with the following goals
1. Reduce the size of MemProf.h 
2. Avoid including ModuleSummaryIndex just for a couple of types

This patch adds CalleeGuids to the serialized format and increments the version number to 4. The unit tests are updated to include a new test for v4 and the YAML format is also updated to be able to roundtrip the v4 format.

This patch moves IndexedMemProfReader::deserialize and its subroutines
to IndexedMemProfData.cpp, building on:

  commit 9a8f90dba3f8c25cbb3525a482053d3abcd3fddc
  Author: Kazu Hirata <kazu@google.com>
  Date:   Wed Apr 23 15:39:45 2025 -0700

The intent is as follows:

- Reduce the size of InstrProfReader.cpp.
- Move the subroutines to a separate file because they don't interact
  with anything else in InstrProfReader.cpp.