vim-patch:9.1.0897: filetype: pyrex files are not detected

Problem:  filetype: pyrex files are not detected
Solution: detect '*.pxi' and '*.pyx+' as pyrex filetype
          (user202729)

References:
https://cython.readthedocs.io/en/latest/src/userguide/language_basics.html#cython-file-types
https://www.csse.canterbury.ac.nz/greg.ewing/python/Pyrex/version/Doc/Manual/using_with_c++.html

closes: vim/vim#16136

aa16b30552

Co-authored-by: user202729 <25191436+user202729@users.noreply.github.com>

runtime/lua/vim/filetype.lua

@@ -962,7 +962,9 @@ local extension = {
   purs = 'purescript',
   arr = 'pyret',
   pxd = 'pyrex',
+  pxi = 'pyrex',
   pyx = 'pyrex',
+  ['pyx+'] = 'pyrex',
   pyw = 'python',
   py = 'python',
   pyi = 'python',

test/old/testdir/test_filetype.vim

@@ -610,7 +610,7 @@ func s:GetFilenameChecks() abort
     \ 'purescript': ['file.purs'],
     \ 'pymanifest': ['MANIFEST.in'],
     \ 'pyret': ['file.arr'],
-    \ 'pyrex': ['file.pyx', 'file.pxd'],
+    \ 'pyrex': ['file.pyx', 'file.pxd', 'file.pxi', 'file.pyx+'],
     \ 'python': ['file.py', 'file.pyw', '.pythonstartup', '.pythonrc', '.python_history', '.jline-jython.history', 'file.ptl', 'file.pyi', 'SConstruct'],
     \ 'ql': ['file.ql', 'file.qll'],
     \ 'qml': ['file.qml', 'file.qbs'],