Highlight git/VCS modified files in explorer, palette, and buffer tabs

[claytonrcarter]

• Added an entry to CHANGELOG.md if this change could be valuable to users

Hi there! I'm enjoying using Lapce and excited to contribute to the project. This PR upates the styling of file names in the file explorer, file palette, and editor tab headers to reflect their curreng git/VCS status. I found this feature really useful in Atom (RIP). I've been using this locally for several days, and it has been accurate and stable so far.

Screenshot showing updated styling:

Notes:

• no new system calls were needed; the data was already present on LapceTabData.file_diffs, it just needed to be tweaked a little to be accessible where needed
• LapceTabData.file_diffs is currently a Vec<(FileDiff, bool)>; this changes it to a HashMap<PathBuf, FileDiff> (for easy lookup by path) and adds a new file_list: Vec<(PathBuf, bool)> to support the int based indexing that's happening on the Vec
• modified, added, deleted are highlighted, along with their containing directories
  • note that directories are only displayed as modified, not added or deleted

Specific things to look for during review:

• I don't expect a performance hit, but perhaps a limited memory usage increase. I'm not able to quantify that at this time, though. Any insight you have here would be great.
• I think I picked the right theme colors, but this should definitely be confirmed.
• I've only been working w/ Lapce for a week or so, so I likely did something very wrong somewhere in here. All suggestions are very welcome!

References:

• Improved Git Integration #793 (comment)
• Feature: error/warn/info hint in File Explorer next to file name #532 (comment)

[codecov-commenter]

Codecov Report

Merging #1856 (6eb9a07) into master (1c7815b) will decrease coverage by 0.01%.
The diff coverage is 0.00%.

@@            Coverage Diff            @@
##           master   #1856      +/-   ##
=========================================
- Coverage    6.94%   6.93%   -0.02%     
=========================================
  Files         128     128              
  Lines       55532   55636     +104     
=========================================
  Hits         3857    3857              
- Misses      51675   51779     +104     

Impacted Files	Coverage Δ
lapce-data/src/data.rs	0.00% <0.00%> (ø)
lapce-data/src/editor.rs	0.00% <0.00%> (ø)
lapce-data/src/palette.rs	4.16% <0.00%> (-0.02%)	⬇️
lapce-data/src/source_control.rs	0.00% <0.00%> (ø)
lapce-ui/src/editor/tab_header_content.rs	12.48% <0.00%> (-0.07%)	⬇️
lapce-ui/src/explorer.rs	0.00% <0.00%> (ø)
lapce-ui/src/palette.rs	0.00% <0.00%> (ø)
lapce-ui/src/source_control.rs	0.00% <0.00%> (ø)
lapce-ui/src/tab.rs	0.00% <0.00%> (ø)
lapce-ui/src/app.rs	0.00% <0.00%> (ø)
... and 5 more

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[claytonrcarter]

Oops, I forgot to include a screenshot of these changes in action when I opened this PR:

[dzhou121]

Excellent work! Thanks!