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: #18566

Signed-off-by: Dragan Simic <dsimic@manjaro.org>
Signed-off-by: Marshall Ward <marshall.ward@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

Author: Dragan Simic

runtime/doc/syntax.txt

@@ -1,4 +1,4 @@
-*syntax.txt*	For Vim version 9.1.  Last change: 2025 Oct 12
+*syntax.txt*	For Vim version 9.1.  Last change: 2025 Oct 13
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -3382,6 +3382,9 @@ 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						*rexx.vim* *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