runtime(vim): make &indentexpr available from the outside

closes: #14936

Signed-off-by: Christian Brabandt <[email protected]>

runtime/indent/vim.vim

@@ -3,7 +3,7 @@ vim9script
 # Vim indent file
 # Language:	Vim script
 # Maintainer:	The Vim Project <https://github.com/vim/vim>
-# Last Change:	2023 Aug 10
+# Last Change:	2024 Jul 12
 # Former Maintainer:	Bram Moolenaar <[email protected]>
 
 # Only load this indent file when no other was loaded.
@@ -16,7 +16,9 @@ b:undo_indent = 'setlocal indentkeys< indentexpr<'
 
 import autoload '../autoload/dist/vimindent.vim'
 
-setlocal indentexpr=vimindent.Expr()
+# export indentexpr as a global function, so it can be easily manipulated by plugins
+g:VimIndent = vimindent.Expr
+setlocal indentexpr=g:VimIndent()
 setlocal indentkeys+==endif,=enddef,=endfu,=endfor,=endwh,=endtry,=endclass,=endinterface,=endenum,=},=else,=cat,=finall,=END,0\\
 execute('setlocal indentkeys+=0=\"\\\ ,0=#\\\ ')
 setlocal indentkeys-=0#