Add line_ending setting to control line-ending normalization

[melocene]

Closes #49581

Adds a line_ending language setting that controls how line endings are handled for new files and during format/save:

• detect (default) — detects existing line endings; new files use the platform default
• prefer_lf / prefer_crlf — sets LF or CRLF for new files and files with no existing convention, while preserving existing files
• enforce_lf / enforce_crlf — normalizes all line endings to LF or CRLF on every format/save

The setting can be configured globally, per-language, or via .editorconfig's end_of_line property (which maps to enforce_lf / enforce_crlf).

Release Notes:

• Added line_ending setting to control how line endings are handled for new files and normalized on save.
• Added support for .editorconfig end_of_line property to enforce line endings.

[smitbarmase]

Thanks, I made few improvements.

• I think that always enforcing these line endings on format and save might not be the best option for everyone, specifically in cases where you might be editing a file from a different operating system and you don't want to change its line endings, while still enforcing the line endings for new files.
• Also, I made a fix for when you create new buffer, it respects your line ending settings.

I introduced two new possibilities for this enum. I think it's better than what VS Code does.

Enum	New empty file	Existing LF file on format/save	Existing CRLF file on format/save	No-convention file on format/save
preserve	Use platform default for the buffer indicator: LF on Unix/macOS/Linux, CRLF on Windows	Stay LF	Stay CRLF	No normalization
prefer_lf	Start as LF	Stay LF	Stay CRLF	Become LF
prefer_crlf	Start as CRLF	Stay LF	Stay CRLF	Become CRLF
enforce_lf	Start as LF	Stay LF	Rewrite to LF	Become LF
enforce_crlf	Start as CRLF	Rewrite to CRLF	Stay CRLF	Become CRLF

Thanks again for working on this! This was a long-awaited feature.

[melocene]

@smitbarmase Thanks for the enhancement to this. I also like that it is now in the settings UI too which is great. I initially tried to follow the existing pattern behavior which is why it wasn't as granular.