vim-patch:9.1.0998: filetype: TI assembly files are not recognized (#31929)

Problem:  filetype: TI assembly files are not recognized
Solution: inspect '*.sa' and assembly files and detect TI assembly
          files, include filetype plugin and syntax script for TI
          assembly files (Wu, Zhenyu)

closes: vim/vim#15827

4f73c07abf

Co-authored-by: Wu, Zhenyu <wuzhenyu@ustc.edu>

test/old/testdir/test_filetype.vim

@@ -672,7 +672,6 @@ func s:GetFilenameChecks() abort
     \ 'samba': ['smb.conf'],
     \ 'sas': ['file.sas'],
     \ 'sass': ['file.sass'],
-    \ 'sather': ['file.sa'],
     \ 'sbt': ['file.sbt'],
     \ 'scala': ['file.scala'],
     \ 'scheme': ['file.scm', 'file.ss', 'file.sld', 'file.stsg', 'any/local/share/supertux2/config', '.lips_repl_history'],
@@ -2322,6 +2321,22 @@ func Test_cmd_file()
   filetype off
 endfunc
 
+func Test_sa_file()
+  filetype on
+
+  call writefile([';* XXX-a.sa: XXX for TI C6000 DSP *;', '.no_mdep'], 'Xfile.sa')
+  split Xfile.sa
+  call assert_equal('tiasm', &filetype)
+  bwipe!
+
+  call writefile(['-- comment'], 'Xfile.sa')
+  split Xfile.sa
+  call assert_equal('sather', &filetype)
+  bwipe!
+
+  filetype off
+endfunc
+
 func Test_sig_file()
   filetype on