vim-patch:9.1.1909: filetype: .mom files recognized as nroff files (#36543)

Problem:  filetype: .mom files recognized as nroff files
Solution: Detect *.mom files as groff filetype instead
          (Callum Andrew)

Reference:
- mom macros are written specifically for groff:
  https://www.schaffter.ca/mom/

closes: vim/vim#18718

23e12c0b7e

Co-authored-by: Callum Andrew <dev@candrew.net>

runtime/lua/vim/filetype.lua

@@ -549,6 +549,8 @@ local extension = {
   graphql = 'graphql',
   graphqls = 'graphql',
   gretl = 'gretl',
+  groff = 'groff',
+  mom = 'groff',
   gradle = 'groovy',
   groovy = 'groovy',
   gsp = 'gsp',
@@ -874,7 +876,6 @@ local extension = {
   roff = 'nroff',
   tmac = 'nroff',
   man = 'nroff',
-  mom = 'nroff',
   nr = 'nroff',
   tr = 'nroff',
   nsi = 'nsis',