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/ftplugin/uci.vim

@@ -0,0 +1,21 @@
+" Vim ftplugin file
+" Language:	OpenWrt Unified Configuration Interface
+" Maintainer:	Colin Caine <complaints@cmcaine.co.uk>
+" Upstream:	https://github.com/cmcaine/vim-uci
+" Last Change:	2024 Apr 17
+"
+" For more information on uci, see https://openwrt.org/docs/guide-user/base-system/uci
+
+if exists("b:did_ftplugin")
+  finish
+endif
+let b:did_ftplugin = 1
+
+" UCI files are indented with tabs.
+setl noexpandtab
+setl shiftwidth=0
+setl softtabstop=0
+
+setl commentstring=#\ %s
+
+let b:undo_ftplugin = "setlocal et< cms< sts< sw<"