vim-patch:9.1.1231: filetype: SPA JSON files are not recognized

Problem:  filetype: SPA (single page application) JSON files are not
          recognized (used by pipewire and wireplumber)
Solution: detect pipewire and wireplumber configuration files as spajson
          filetype, include filetype, indent and syntax scripts for this
          new filetype (David Mandelberg).

I looked at all the files found by this command to see if the syntax
highlighting looked reasonable:

```
find {~/.config,/etc,/usr/share}/{pipewire,wireplumber} -type f -name \*.conf
```

References:
*   pipewire config files: https://docs.pipewire.org/page_config.html
*   wireplumber config files:
    https://pipewire.pages.freedesktop.org/wireplumber/daemon/configuration/conf_file.html
    and
*   https://pipewire.pages.freedesktop.org/wireplumber/daemon/locations.html

closes: vim/vim#16950

4e7b4308fb

Co-authored-by: David Mandelberg <david@mandelberg.org>

test/old/testdir/test_filetype.vim

@@ -719,6 +719,8 @@ func s:GetFilenameChecks() abort
     \ 'snobol4': ['file.sno', 'file.spt'],
     \ 'solidity': ['file.sol'],
     \ 'solution': ['file.sln'],
+    \ 'spajson': ['any/pipewire/file.conf', 'any/pipewire/file.conf.d/other.conf',
+    \             'any/wireplumber/file.conf', 'any/wireplumber/file.conf.d/other.conf'],
     \ 'sparql': ['file.rq', 'file.sparql'],
     \ 'spec': ['file.spec'],
     \ 'spice': ['file.sp', 'file.spice'],