[clang] [clang][analyzer] Bring alpha.security.MmapWriteExec checker out of alpha package (PR #102636)

[Balazs Benics via cfe-commits]

steakhal wrote:

`nasm`, `breakpad`, `tinycbor`, `snappy`, `ffmpeg`, `libxml`, `tflite`, `tensorflow`, `abseil-cpp`, `LibreOffice`, `Redis`, `mongodb`, `PostgreSQL`, `rocksdb`, `aragondb`, `MySQL`, `HHVM`, `nginx`, `zfs`, `zstd`, `Clang/compiler-rt`, `transmission`, `OpenSSL` [and more] appears to reference `mmap` directly or transitively.

https://github.com/llvm/llvm-project/pull/102636