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_bool_constant_00.dump

@@ -0,0 +1,20 @@
+>/+0#0000e05#ffffff0@1| |C| |b|o@1|l|e|a|n| |c|o|n|s|t|a|n|t|s| +0#0000000&@52
+@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|/|b|o@1|l|_|c|o|n|s|t|a|n|t| +0#0000000&@9
+@75
+|#+0#e000e06&|i|n|c|l|u|d|e| |<+0#e000002&|a|s@1|e|r|t|.|h|>| +0#0000000&@55
+@75
+|i+0#00e0003&|n|t| +0#0000000&|m|a|i|n|(|)| @64
+|{| @73
+@4|a|s@1|e|r|t|(|t+0#e000002&|r|u|e| +0#0000000&|=@1| |1+0#e000002&| +0#0000000&|&@1| |0+0#e000002&| +0#0000000&|=@1| |f+0#e000002&|a|l|s|e|)+0#0000000&|;| @38
+|}| @73
+@75
+|~+0#4040ff13&| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+| +0#0000000&@56|1|,|1| @10|A|l@1|