Add support for LilyPond syntax (#5117)

* Add support for LilyPond syntax

See: https://lilypond.org/

* Fix alpha order of LilyPond

* Add support for custom executable and options to lilypond linter

Enhances the lilypond linter with configurable options:
- Add g:ale_lilypond_lilypond_executable for custom lilypond binary path
- Add g:ale_lilypond_lilypond_options for additional command-line flags
- Refactor linter to use GetCommand() function for dynamic command building
- Add linter tests covering configuration scenarios
- Update documentation with usage examples and proper formatting

---------

Co-authored-by: samb0t <sambottoni@gmail.com>

ale_linters/lilypond/lilypond.vim

@@ -0,0 +1,40 @@
+" Author: Sam Bottoni
+" Description: lilypond linter for LilyPond files
+
+call ale#Set('lilypond_lilypond_executable', 'lilypond')
+
+let g:ale_lilypond_lilypond_options = get(g:, 'ale_lilypond_lilypond_options', '')
+
+function! ale_linters#lilypond#lilypond#GetCommand(buffer) abort
+    return '%e --loglevel=WARNING -dbackend=null -dno-print-pages -o /tmp'
+    \   . ale#Pad(ale#Var(a:buffer, 'lilypond_lilypond_options'))
+    \   . ' %t 2>&1'
+endfunction
+
+function! ale_linters#lilypond#lilypond#Handle(buffer, lines) abort
+    let l:output = []
+
+    for l:line in a:lines
+        " Match: file:line:col: error|warning|programming error: message
+        let l:match = matchlist(l:line,
+        \   '\v^.*:(\d+):(\d+): (error|warning|programming error): (.*)$')
+
+        if !empty(l:match)
+            call add(l:output, {
+            \   'lnum': str2nr(l:match[1]),
+            \   'col': str2nr(l:match[2]),
+            \   'type': l:match[3] =~? 'error' ? 'E' : 'W',
+            \   'text': l:match[4]
+            \})
+        endif
+    endfor
+
+    return l:output
+endfunction
+
+call ale#linter#Define('lilypond', {
+\   'name': 'lilypond',
+\   'executable': {b -> ale#Var(b, 'lilypond_lilypond_executable')},
+\   'command': function('ale_linters#lilypond#lilypond#GetCommand'),
+\   'callback': 'ale_linters#lilypond#lilypond#Handle',
+\})