Item movers

[ivan770]

Closes #6823

moveitem.mp4

Implementation issues:

• Most of items are non-movable, since movability of any item has to be determined manually. Common ones are movable though
• Cursor should move with the item

[lnicola]

changelog feature add "Move item up/down" commands (LSP extension)

[ivan770]

Demo with improved cursor movement and ArgList mover

demoupd.mp4

Adding similar movers should be trivial

[matklad]

bors r+

This actually is very reasonable, sorry for not getting to review this earlier, this could have landed in today's release.

[bors]

Build succeeded:

• Rust (macos-latest)
• Rust (ubuntu-latest)
• Rust (windows-latest)
• TypeScript (ubuntu-latest)
• TypeScript (windows-latest)

[puremourning]

What was the rationale for this being a custom message instead of code action?

[ivan770]

What was the rationale for this being a custom message instead of code action?

Is it possible to provide a direction in which we are moving an item via code action?

[puremourning]

Have one action for up and one for down?

[matklad]

I don't think code action UI is right here: code actions should be available in narrow scope, while this is an always available thing. In IntelliJ, item movers are also a separate thing with dedicated shortcuts.

Using code-actions API for this might be interesting (ie, the editor still doesn't show these in code action list, and binds them to dedicated shortcuts, but internally it issues code action requests), but I am not entirely sure if that would be a good move. Sticking to LSP's "one request for one UI concern" rule of thumb is more compatible with potential future extensions (multible cursors, left-right movers, etc).

[lnicola]