Add frontend handling for move line

[nangtrongvuon]

This adds frontend support for moving lines.

The default hotkeys are Alt + Up/Down for move lines up/down respectively.

Depends on xi-core's #849.

[cmyr]

Looks good, feel free to merge this whenever the core PR goes in. 😎

[codecov-io]

Codecov Report

Merging #278 into master will decrease coverage by 1.9%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master     #278      +/-   ##
==========================================
- Coverage   45.87%   43.96%   -1.91%     
==========================================
  Files          30       30              
  Lines        3863     3867       +4     
==========================================
- Hits         1772     1700      -72     
- Misses       2091     2167      +76

Impacted Files	Coverage Δ
Sources/XiEditor/EditViewController.swift	27.2% <0%> (-10.83%)	⬇️
Sources/XiEditor/AppDelegate.swift	35.29% <0%> (-4.42%)	⬇️
Sources/XiEditor/XiTextPlane/Atlas.swift	76.78% <0%> (-1.79%)	⬇️
Sources/XiEditor/EditView.swift	54.44% <0%> (-0.86%)	⬇️

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