runtime(c): Update syntax and ftplugin files

- highlight more C keywords, including some from C23

Conditionally highlight C23 features:
- #embed, #elifdef and #elifndef preprocessor directives
- predefined macros
- UTF-8 character constants
- binary integer constants, _BitInt literals, and digit separators
- nullptr_t type and associated constant
- decimal real floating-point, bit precise and char types
- typeof operators

Matchit:
- update for new preprocessor directives

fixes: #13667
fixes: #13679
closes: #12984

Co-authored-by: Albin Ahlbäck <albin.ahlback@gmail.com>
Signed-off-by: Doug Kearns <dougkearns@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/syntax/testdir/dumps/c_string_literal_00.dump

@@ -0,0 +1,20 @@
+>/+0#0000e05#ffffff0@1| |C| |s|t|r|i|n|g| |l|i|t|e|r|a|l|s| +0#0000000&@54
+@75
+|/+0#0000e05&@1| |S|o|u|r|c|e|:| |h|t@1|p|s|:|/@1|e|n|.|c|p@1|r|e|f|e|r|e|n|c|e|.|c|o|m|/|w|/|c|/|l|a|n|g|u|a|g|e|/|s|t|r|i|n|g|_|l|i|t|e|r|a|l| +0#0000000&@8
+@75
+|#+0#e000e06&|i|n|c|l|u|d|e| |<+0#e000002&|i|n|t@1|y|p|e|s|.|h|>| +0#0000000&@53
+|#+0#e000e06&|i|n|c|l|u|d|e| |<+0#e000002&|l|o|c|a|l|e|.|h|>| +0#0000000&@55
+|#+0#e000e06&|i|n|c|l|u|d|e| |<+0#e000002&|s|t|d@1|e|f|.|h|>| +0#0000000&@55
+|#+0#e000e06&|i|n|c|l|u|d|e| |<+0#e000002&|s|t|d|i|o|.|h|>| +0#0000000&@56
+|#+0#e000e06&|i|n|c|l|u|d|e| |<+0#e000002&|s|t|d|l|i|b|.|h|>| +0#0000000&@55
+|#+0#e000e06&|i|n|c|l|u|d|e| |<+0#e000002&|u|c|h|a|r|.|h|>| +0#0000000&@56
+@75
+|i+0#00e0003&|n|t| +0#0000000&|m|a|i|n|(|v+0#00e0003&|o|i|d|)+0#0000000&| @60
+|{| @73
+@4|c+0#00e0003&|h|a|r| +0#0000000&|s|1|[|]| |=| |"+0#e000002&|a|猫*&|🍌|"+&|;+0#0000000&| |/+0#0000e05&@1| |o|r| |"|a|\|u|7|3|2|B|\|U|0@2|1|F|3|4|C|"| +0#0000000&@24
+|#+0#e000e06&|i|f| |_@1|S|T|D|C|_|V|E|R|S|I|O|N|_@1| |>|=| |2+0#e000002&|0|2|3|1@1|L| +0#0000000&@43
+@4|c+0#00e0003&|h|a|r|8|_|t| +0#0000000&@63
+|#+0#e000e06&|e|l|s|e| +0#0000000&@69
+@4|c+0#00e0003&|h|a|r| +0#0000000&@66
+|#+0#e000e06&|e|n|d|i|f| +0#0000000&@68
+@57|1|,|1| @10|T|o|p|