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_03.dump

@@ -17,4 +17,4 @@
 |a+0#e000002&|n|d| |\+0#e000e06&|u|0@1|A|1| +0#e000002&|a|n|d| |\+0#e000e06&|U|0@2|1|0|6|0|5|"+0#e000002&@2| +0#0000000&@46
 @75
 |#+0#0000e05&| |F|o|r|m|a|t@1|e|d| |s|t|r|i|n|g| |l|i|t|e|r|a|l|s| |(|f|-|s|t|r|i|n|g|s|)| +0#0000000&@35
-@57|4|9|,|1| @9|3|8|%| 
+@57|4|9|,|1| @9|2|4|%|