patch 9.1.0354: runtime(uci): No support for uci file types

Problem:  runtime(uci): No support for uci file types
          (Wu, Zhenyu)
Solution: include basic uci ftplugin and syntax plugins
          (Colin Caine)

closes: #14575

Co-authored-by: Wu, Zhenyu <wuzhenyu@ustc.edu>
Signed-off-by: Colin Caine <complaints@cmcaine.co.uk>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/syntax/uci.vim

@@ -0,0 +1,33 @@
+" Vim syntax file
+" Language:	OpenWrt Unified Configuration Interface
+" Maintainer:	Colin Caine <complaints@cmcaine.co.uk>
+" Upstream:	https://github.com/cmcaine/vim-uci
+" Last Change:	2021 Sep 19
+"
+" For more information on uci, see https://openwrt.org/docs/guide-user/base-system/uci
+
+if exists("b:current_syntax")
+    finish
+endif
+
+" Fancy zero-width non-capturing look-behind to see what the last word was.
+" Would be really nice if there was some less obscure or more efficient way to
+" do this.
+syntax match uciOptionName '\%(\%(option\|list\)\s\+\)\@<=\S*'
+syntax match uciConfigName '\%(\%(package\|config\)\s\+\)\@<=\S*'
+syntax keyword uciConfigDec package config nextgroup=uciConfigName skipwhite
+syntax keyword uciOptionType option list nextgroup=uciOptionName skipwhite
+
+" Standard matches.
+syntax match uciComment "#.*$"
+syntax region uciString start=+"+ end=+"+ skip=+\\"+
+syntax region uciString start=+'+ end=+'+ skip=+\\'+
+
+highlight default link uciConfigName Identifier
+highlight default link uciOptionName Constant
+highlight default link uciConfigDec Statement
+highlight default link uciOptionType Type
+highlight default link uciComment Comment
+highlight default link uciString Normal
+
+let b:current_syntax = "uci"