patch 9.1.0592: runtime: filetype: Mediawiki files are not recognized

Problem:  filetype: Mediawiki files are not recognized
Solution: detect "*.mw" and "*.wiki" as mediawiki filetype,
          include basic syntax and filetype plugins.
          (AvidSeeker)

closes: #15266

Signed-off-by: AvidSeeker <avidseeker7@protonmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/ftplugin/mediawiki.vim

@@ -0,0 +1,42 @@
+" Language: MediaWiki
+" Maintainer: Avid Seeker <avidseeker7@protonmail.com>
+" Home: http://en.wikipedia.org/wiki/Wikipedia:Text_editor_support#Vim
+" Last Change: 2024 Jul 14
+" Credits: chikamichi
+"
+
+if exists("b:did_ftplugin")
+  finish
+endif
+let g:did_ftplugin = 1
+
+" Many MediaWiki wikis prefer line breaks only at the end of paragraphs
+" (like in a text processor), which results in long, wrapping lines.
+setlocal wrap linebreak
+setlocal textwidth=0
+
+setlocal formatoptions-=tc formatoptions+=l formatoptions+=roq
+setlocal matchpairs+=<:>
+
+" Treat lists, indented text and tables as comment lines and continue with the
+" same formatting in the next line (i.e. insert the comment leader) when hitting
+" <CR> or using "o".
+setlocal comments=n:#,n:*,n:\:,s:{\|,m:\|,ex:\|},s:<!--,m:\ \ \ \ ,e:-->
+setlocal commentstring=<!--\ %s\ -->
+
+" match HTML tags (taken directly from $VIM/ftplugin/html.vim)
+if exists("loaded_matchit")
+    let b:match_ignorecase=0
+    let b:match_skip = 's:Comment'
+    let b:match_words = '<:>,' .
+    \ '<\@<=[ou]l\>[^>]*\%(>\|$\):<\@<=li\>:<\@<=/[ou]l>,' .
+    \ '<\@<=dl\>[^>]*\%(>\|$\):<\@<=d[td]\>:<\@<=/dl>,' .
+    \ '<\@<=\([^/][^ \t>]*\)[^>]*\%(>\|$\):<\@<=/\1>'
+endif
+
+" Enable folding based on ==sections==
+setlocal foldexpr=getline(v:lnum)=~'^\\(=\\+\\)[^=]\\+\\1\\(\\s*<!--.*-->\\)\\=\\s*$'?\">\".(len(matchstr(getline(v:lnum),'^=\\+'))-1):\"=\"
+setlocal foldmethod=expr
+
+let b:undo_ftplugin = "setl commentstring< comments< formatoptions< foldexpr< foldmethod<"
+let b:undo_ftplugin += " matchpairs< linebreak< wrap< textwidth<"