vim-patch:9.2.0836: filetype: .git-blame-ignore-revs file is not recognized (#40912)

Problem:  filetype: .git-blame-ignore-revs file is not recognized
Solution: Detect .git-blame-ignore-revs file as gitrevlist filetype,
          include syntax and filetype plugins (Fionn Fitzmaurice)

A Git revision list is

> a list of object names (i.e. one unabbreviated SHA-1 per line)...,
> comments (#), empty lines, and any leading and trailing whitespace are
> ignored.

(from Git's fsck.skipList documentation).

The default output of git rev-list will match this. It is also suitable
as input to git blame --ignore-revs-file.

This adds filetype detection matching .git-blame-ignore-revs files,
syntax highlighting and basic filetype settings.

closes: vim/vim#20702

a8d5be9284

Co-authored-by: Fionn Fitzmaurice <fionn@github.com>

runtime/lua/vim/filetype.lua

@@ -1730,6 +1730,7 @@ local filename = {
   ['.vscodeignore'] = 'gitignore',
   ['gitolite.conf'] = 'gitolite',
   ['git-rebase-todo'] = 'gitrebase',
+  ['.git-blame-ignore-revs'] = 'gitrevlist',
   gkrellmrc = 'gkrellmrc',
   ['.gnashrc'] = 'gnash',
   ['.gnashpluginrc'] = 'gnash',