When providing allocation and deallocation traces,
the ASan compiler-rt runtime already provides call
addresses (`TracePCType::Calls`).

On Darwin, system sanitizers (libsanitizers)
provides return address.  It also discards a few
non-user frames at the top of the stack, because
these internal libmalloc/libsanitizers stack
frames do not provide any value when diagnosing
memory errors.

Introduce and add handling for
`TracePCType::ReturnsNoZerothFrame` to cover this
case and enable libsanitizers traces line-level
testing.

rdar://157596927

---
Commit 1 is a mechanical refactoring to introduce
and adopt `TracePCType` enum to replace
`pcs_are_call_addresses` bool.  It preserve the
current behavior:
```
pcs_are_call_addresses:
  false  ->  TracePCType::Returns (default)
  true   ->  TracePCType::Calls
``` 

Best reviewed commit by commit.

The regex we use to find the compiler-rt library is already
Darwin-specific, so no need to run this on non-Darwin platforms.

These weren't rendering properly (mostly mis-use the syntax for
commenting member variables).

The `TestMemoryHistory.py`/`TestReportData.py` are currently failing on
the x86 macOS CI (started after we upgraded the Xcode SDK on that
machien). The LLDB ASAN utility expression is failing to run with
following error:
```
(lldb) image lookup -n __asan_get_alloc_stack
1 match found in /usr/lib/system/libsystem_sanitizers.dylib:
        Address: libsystem_sanitizers.dylib[0x00007ffd11e673f7] (libsystem_sanitizers.dylib.__TEXT.__text + 11287)
        Summary: libsystem_sanitizers.dylib`__asan_get_alloc_stack
1 match found in /Users/michaelbuch/Git/lldb-build-main-no-modules/lib/clang/21/lib/darwin/libclang_rt.asan_osx_dynamic.dylib:
        Address: libclang_rt.asan_osx_dynamic.dylib[0x0000000000009ec0] (libclang_rt.asan_osx_dynamic.dylib.__TEXT.__text + 34352)
        Summary: libclang_rt.asan_osx_dynamic.dylib`::__asan_get_alloc_stack(__sanitizer::uptr, __sanitizer::uptr *, __sanitizer::uptr, __sanitizer::u32 *) at asan_debugging.cpp:132
(lldb) memory history 'pointer'
Assertion failed: ((uintptr_t)addr == report.access.address), function __asan_get_alloc_stack, file debugger_abi.cpp, line 62.
warning: cannot evaluate AddressSanitizer expression:
error: Expression execution was interrupted: signal SIGABRT.
The process has been returned to the state before expression evaluation.
```

The reason for this is that the system sanitizer dylib and the locally
built libclang_rt contain the same symbol `__asan_get_alloc_stack`, and
depending on the order in which they're loaded, we may pick the one from
the wrong dylib (this probably changed during the buildbot upgrade and
is why it only now started failing). Based on discussion with @wrotki we
always want to pick the one that's in the libclang_rt dylib if it was
loaded, and libsystem_sanitizers otherwise.

This patch addresses this by adding a "preferred lookup context list" to
the expression evaluator. Currently this is only exposed in the
`EvaluateExpressionOptions`. We make it a `SymbolContextList` in case we
want the lookup contexts to be contexts other than modules (e.g., source
files, etc.). In `IRExecutionUnit` we make it a `ModuleList` because it
makes the symbol lookup implementation simpler and we only do module
lookups here anyway. If we ever need it to be a `SymbolContext`, that
transformation shouldn't be too difficult.