runtime(nu): Add new Nushell runtime files

See: https://github.com/elkasztano/nushell-syntax-vim

Thanks to Pete Cruz (@Petesta) for promoting this addition.

closes: #18208

Signed-off-by: Doug Kearns <dougkearns@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/indent/nu.vim

@@ -0,0 +1,54 @@
+" Vim indent file
+" Language:	Nushell
+" Maintainer:	El Kasztano
+" URL:		https://github.com/elkasztano/nushell-syntax-vim
+" License:	MIT <https://opensource.org/license/mit>
+" Last Change:	2025 Sep 05
+
+" Only load if no other indent file is loaded
+if exists("b:did_indent")
+  finish
+endif
+let b:did_indent = 1
+
+setlocal cindent
+setlocal cinoptions=L0,(s,Ws,J1,j1,+0,f5,m1,i0
+setlocal cinkeys=0{,0},!^F,o,O,0[,0],0),0#
+
+setlocal autoindent
+setlocal indentkeys=0{,0},!^F,o,O,0[,0],0),0#
+
+setlocal shiftwidth=2
+setlocal softtabstop=2
+setlocal expandtab
+
+setlocal indentexpr=GetNuIndent(v:lnum)
+
+let b:undo_indent = "setl ai< cin< cink< cino< et< inde< indk< sts< sw<"
+
+" only define once
+if exists("*GetNuIndent")
+  finish
+endif
+
+let s:save_cpo = &cpo
+set cpo&vim
+
+function GetNuIndent(lnum)
+	let prevlnum = prevnonblank(v:lnum - 1) "get number of last non blank line
+	let line = getline(a:lnum)
+	let synname = synIDattr(synID(a:lnum, 1, 1), "name")
+	if (synname == "nuString") || (synname == "nuComment")
+		return -1
+	endif
+	if getline(prevlnum) =~ '\%(^.*[$\|^.*[\s*#.*$\)'
+		return (prevlnum > 0) * indent(prevlnum) + shiftwidth()
+	endif
+	if getline(v:lnum) =~ "^\s*]\>"
+		return (prevlnum > 0) * indent(prevlnum) - shiftwidth()
+	endif
+	return cindent(a:lnum)
+endfunction
+
+let &cpo = s:save_cpo
+unlet s:save_cpo