runtime(arduino): Add Arduino ftplugin and indent files (#14811)

We already have Arduino syntax file, but we didn't have ftplugin and
indent files.

This commit adds a basic ftplugin file and a basic indent file.
Both of them are derived from {ftplugin,indent}/c.vim.

Signed-off-by: Ken Takata <kentkt@csc.jp>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/.github/MAINTAINERS b/.github/MAINTAINERS
index f09b2c9..a97d18d 100644
--- a/.github/MAINTAINERS
+++ b/.github/MAINTAINERS
@@ -106,6 +106,7 @@
 runtime/doc/ps1.txt			@heaths
 runtime/ftplugin/abaqus.vim		@costerwi
 runtime/ftplugin/apache.vim		@dubgeiser 
+runtime/ftplugin/arduino.vim		@k-takata
 runtime/ftplugin/astro.vim		@romainl
 runtime/ftplugin/awk.vim		@dkearns
 runtime/ftplugin/basic.vim		@dkearns
@@ -243,6 +244,7 @@
 runtime/ftplugin/xs.vim			@petdance
 runtime/ftplugin/zsh.vim		@chrisbra
 runtime/import/dist/vimhighlight.vim	@lacygoill
+runtime/indent/arduino.vim		@k-takata
 runtime/indent/astro.vim		@wuelnerdotexe
 runtime/indent/basic.vim		@dkearns
 runtime/indent/bst.vim			@tpope