### What problem does this PR solve?
When multiple columns are used as content columns in RDBMS connector,
the generated document text gets chunked by TxtParser which strips
newline delimiters during merge. This causes field names and values from
different columns to be concatenated without any separator, making the
content unreadable.
Changes:
- txt_parser.py: restore newline separator when merging adjacent text
segments within a chunk, so that split sections are not directly
concatenated
- rdbms_connector.py: use double newline between fields and place field
value on a new line after the field name bracket, giving TxtParser
clearer boundaries to work with
Closes#13001
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
Co-authored-by: tunsuytang <tunsuytang@tencent.com>
### What problem does this PR solve?
Fix special delimiter parsing issue #5382
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
### What problem does this PR solve?
Add get_txt function to reduce duplicate code
### Type of change
- [x] Refactoring
---------
Co-authored-by: Kevin Hu <kevinhu.sh@gmail.com>
### What problem does this PR solve?
### Type of change
- [ ] Bug Fix (non-breaking change which fixes an issue)
- [x] New Feature (non-breaking change which adds functionality)
### What problem does this PR solve?
add support for eml file parser
#1363
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
---------
Co-authored-by: Zhedong Cen <cenzhedong2@126.com>
Co-authored-by: Kevin Hu <kevinhu.sh@gmail.com>
