Add meson format

**Formatter tool**
[`meson format`](https://mesonbuild.com/Commands.html#format)

**Filetype(s)**
`meson`

**Additional context**
N/A

Start by reading the existing formatter integrations in vim-codefmt and the linked Meson format documentation, then find how a formatter is associated with the `meson` filetype. Done means `meson` files are recognized and formatted through `meson format`, with coverage matching the repository's existing formatter behavior.

Written by the indexing model from the issue text.