vim-patch:310082f: runtime(rst): Add support for rst_minlines

Following the approach used in other syntax definitions, add support for
defining the "syntax sync minlines=..." values for rst files in the
users' ~/.vimrc files, to allow the users to adjust that value in case
syntax highlighting stops working for some of the files they edit.

related: vim/vim#18566

310082f3cf

Co-authored-by: Dragan Simic <dsimic@manjaro.org>

runtime/doc/syntax.txt

@@ -2892,6 +2892,9 @@ To enable folding of sections: >
 
 Note that folding can cause performance issues on some platforms.
 
+The minimum line syntax sync is set to 50.  To modify this number: >
+	let rst_minlines = 100
+
 
 REXX							*ft-rexx-syntax*
 

runtime/syntax/rst.vim

@@ -246,11 +246,11 @@ for s:filetype in keys(g:rst_syntax_code_list)
     unlet! prior_isk
 endfor
 
+
 " Enable top level spell checking
 syntax spell toplevel
 
-" TODO: Use better syncing.
-syn sync minlines=50 linebreaks=2
+exe "syn sync minlines=" . get(g:, 'rst_minlines', 50) . " linebreaks=2"
 
 hi def link rstTodo                         Todo
 hi def link rstComment                      Comment