runtime(python): Highlight f-string replacement fields in Python

Highlight f-string replacement fields, including

- Comments
- Debugging flags
- Conversion fields
- Format specifications
- Delimiters

Syntax inside fields will be addressed in a separate commit.

related: #10734
related: #14033
closes: #17784

Signed-off-by: Rob B <github@0x7e.net>
Signed-off-by: Zvezdan Petkovic <zpetkovic@acm.org>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/syntax/testdir/dumps/python_strings_bytes_01.dump

@@ -17,4 +17,4 @@
 |a+0#e000002&|n|d| |l|i|t|e|r|a|l| |\|t| |a|n|d| |\|0|4|0| |a|n|d| |\|x|F@1| +0#0000000&@42
 |a+0#e000002&|n|d| |l|i|t|e|r|a|l| |\|u|0@1|A|1| |a|n|d| |\|U|0@2|1|0|6|0|5|"@2| +0#0000000&@38
 @75
-@57|1|7|,|1| @10|9|%| 
+@57|1|7|,|1| @10|6|%|