Add support for meson.options

[LNSD]

Since meson v1.1.0, the meson_options.txt has been renamed to meson.options. See:

• https://mesonbuild.com/Build-options.html#build-options

  [...] Its name is meson.options and it is placed at the root of your source tree. For versions of meson before 1.1, this file was called meson_options.txt.

• https://mesonbuild.com/Release-notes-for-1-1-0.html#support-for-reading-options-from-mesonoptions

  Support has been added for reading options from meson.options instead of meson_options.txt. These are equivalent, but not using the .txt extension for a build file has a few advantages, chief among them many tools and text editors expect a file with the .txt extension to be plain text files, not build scripts.

This pull request updates the way Meson build option files are identified and tagged. The main changes involve recognizing both meson.options and meson_options.txt files as Meson option files and updating their associated tags accordingly.

[asottile]