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>

doc/ale-lilypond.txt

@@ -0,0 +1,29 @@
+===============================================================================
+ALE LilyPond Integration                                 *ale-lilypond-options*
+
+
+===============================================================================
+lilypond                                                         *ale-lilypond*
+
+g:ale_lilypond_lilypond_executable           *g:ale_lilypond_lilypond_executable*
+                                             *b:ale_lilypond_lilypond_executable*
+  Type: |String|
+  Default: `'lilypond'`
+
+  This variable can be changed to modify the executable used for lilypond.
+
+
+g:ale_lilypond_lilypond_options                 *g:ale_lilypond_lilypond_options*
+                                                *b:ale_lilypond_lilypond_options*
+  Type: |String|
+  Default: `''`
+
+  This variable can be changed to modify flags given to lilypond.
+
+  For example, to add custom include paths: >
+
+    let g:ale_lilypond_lilypond_options = '--include=/path/to/includes'
+<
+
+===============================================================================
+  vim:tw=78:ts=2:sts=2:sw=2:ft=help:norl:

doc/ale-supported-languages-and-tools.txt

@@ -383,6 +383,8 @@ Notes:
   * `lessc`
   * `prettier`
   * `stylelint`
+* LilyPond
+  * `lilypond`
 * LLVM
   * `llc`
 * Lua

doc/ale.txt

@@ -3722,6 +3722,8 @@ documented in additional help files.
     lessc.................................|ale-less-lessc|
     prettier..............................|ale-less-prettier|
     stylelint.............................|ale-less-stylelint|
+  lilypond................................|ale-lilypond-options|
+    lilypond..............................|ale-lilypond|
   llvm....................................|ale-llvm-options|
     llc...................................|ale-llvm-llc|
   lua.....................................|ale-lua-options|