Add configurable options support for redpen linter (#5006)

Redpen linter previously had hardcoded command-line options and duplicated
linter definitions across all supported file types (asciidoc, markdown,
review, rst, tex, text). This refactoring centralizes the linter definition
and adds support for user-configurable options via g:ale_redpen_options.

Key changes:
- Created ale#handlers#redpen#DefineLinter() to eliminate code duplication
- Added ale#handlers#redpen#GetCommand() to support configurable options
- All file types now use shared configuration and command building
- Added comprehensive test coverage for option handling
- Updated documentation for all affected file types

This allows users to customize redpen behavior with additional command-line
options while maintaining backward compatibility and reducing maintenance
overhead.

autoload/ale/handlers/redpen.vim

@@ -1,6 +1,8 @@
 " Author: rhysd https://rhysd.github.io
 " Description: Redpen, a proofreading tool (http://redpen.cc)
 
+call ale#Set('redpen_options', '')
+
 function! ale#handlers#redpen#HandleRedpenOutput(buffer, lines) abort
     " Only one file was passed to redpen. So response array has only one
     " element.
@@ -63,3 +65,14 @@ function! ale#handlers#redpen#HandleRedpenOutput(buffer, lines) abort
 
     return l:output
 endfunction
+
+
+" Define the redpen linter for a given filetype.
+function! ale#handlers#redpen#DefineLinter(filetype) abort
+    call ale#linter#Define(a:filetype, {
+    \   'name': 'redpen',
+    \   'executable': 'redpen',
+    \   'command': {b -> 'redpen -f ' . a:filetype . ' -r json' . ale#Pad(ale#Var(b, 'redpen_options')) . ' %t'},
+    \   'callback': 'ale#handlers#redpen#HandleRedpenOutput',
+    \})
+endfunction