[libc] Replace `MutexLock` with `cpp::lock_guard` (#89340)

This PR address issue #89002.

#### Changes in this PR

* Added a simple implementation of `cpp::lock_guard` (an equivalent of
`std::l

[libc] Replace `MutexLock` with `cpp::lock_guard` (#89340)

This PR address issue #89002.

#### Changes in this PR

* Added a simple implementation of `cpp::lock_guard` (an equivalent of
`std::lock_guard`) in libc/src/__support/CPP inspired by the libstdc++
implementation
* Added tests for `cpp::lock_guard` in
/libc/test/src/__support/CPP/mutex_test.cpp
* Replaced all references to `MutexLock` with `cpp::lock_guard`

---------

Co-authored-by: Guillaume Chatelet <gchatelet@google.com>

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