patch 9.1.1177: filetype: tera files not detected

Problem:  filetype: tera files not detected
Solution: detect '*.tera' files as tera filetype,
          include a simple filetype plugin
          (MuntasirSZN)

closes: #16806

Signed-off-by: MuntasirSZN <muntasir.joypurhat@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/filetype.vim

@@ -1,7 +1,7 @@
 " Vim support file to detect file types
 "
 " Maintainer:	The Vim Project <https://github.com/vim/vim>
-" Last Change:	2025 Mar 05
+" Last Change:	2025 Mar 06
 " Former Maintainer:	Bram Moolenaar <Bram@vim.org>
 
 " Listen very carefully, I will say this only once
@@ -2604,6 +2604,9 @@ au BufRead,BufNewFile *.ttl
 " Terminfo
 au BufNewFile,BufRead *.ti			setf terminfo
 
+" Tera
+au BufRead,BufNewFile *.tera			setf tera
+
 " Terraform variables
 au BufRead,BufNewFile *.tfvars			setf terraform-vars
 

runtime/ftplugin/tera.vim

@@ -0,0 +1,13 @@
+" Vim filetype plugin file
+" Language:             Tera
+" Maintainer:           Muntasir Mahmud <muntasir.joypurhat@gmail.com>
+" Last Change:          2025 Mar 06
+
+if exists("b:did_ftplugin")
+  finish
+endif
+let b:did_ftplugin = 1
+
+setlocal commentstring={#\ %s\ #}
+
+let b:undo_ftplugin = "setlocal commentstring<"