[ASan][libc++] Turn on ASan annotations for short strings (#75882)

This commit turns on ASan annotations in `std::basic_string` for short
stings (SSO case).

Originally suggested here: https://reviews.llvm.org/D147680

String annotations added here:
https://github.com/llvm/llvm-project/pull/72677

Requires to pass CI without fails:
- https://github.com/llvm/llvm-project/pull/75845
- https://github.com/llvm/llvm-project/pull/75858

Annotating `std::basic_string` with default allocator is implemented in
https://github.com/llvm/llvm-project/pull/72677 but annotations for
short strings (SSO - Short String Optimization) are turned off there.
This commit turns them on. This also removes
`_LIBCPP_SHORT_STRING_ANNOTATIONS_ALLOWED`, because we do not plan to
support turning on and off short string annotations.

Support in ASan API exists since
https://github.com/llvm/llvm-project/commit/dd1b7b797a116eed588fd752fbe61d34deeb24e4.
You can turn off annotations for a specific allocator based on changes
from
https://github.com/llvm/llvm-project/commit/2fa1bec7a20bb23f2e6620085adb257dafaa3be0.

This PR is a part of a series of patches extending AddressSanitizer C++
container overflow detection capabilities by adding annotations, similar
to those existing in `std::vector` and `std::deque` collections. These
enhancements empower ASan to effectively detect instances where the
instrumented program attempts to access memory within a collection's
internal allocation that remains unused. This includes cases where
access occurs before or after the stored elements in `std::deque`, or
between the `std::basic_string`'s size (including the null terminator)
and capacity bounds.

The introduction of these annotations was spurred by a real-world
software bug discovered by Trail of Bits, involving an out-of-bounds
memory access during the comparison of two strings using the
`std::equals` function. This function was taking iterators
(`iter1_begin`, `iter1_end`, `iter2_begin`) to perform the comparison,
using a custom comparison function. When the `iter1` object exceeded the
length of `iter2`, an out-of-bounds read could occur on the `iter2`
object. Container sanitization, upon enabling these annotations, would
effectively identify and flag this potential vulnerability.

If you have any questions, please email:

    advenam.tacet@trailofbits.com
    disconnect3d@trailofbits.com

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