editor: Add MoveUpByLines and MoveDownByLines actions

[mrnugget]

This adds four new actions:

• editor::MoveUpByLines
• editor::MoveDownByLines
• editor::SelectUpByLines (bound by default to shift-alt-up)
• editor::SelectDownByLines (bound by default to shift-alt-up)

They all take a count by which to move the cursor up and down.

Requested by Adam here: https://twitter.com/adamwathan/status/1753017094248018302

Release Notes:

• Added four new actions: editor::MoveUpByLines, editor::MoveDownByLines, editor::SelectUpByLines (bound by default to shift-alt-up with 3 lines), editor::SelectDownByLines (bound by default to shift-alt-up with 3 lines) that move the cursor up by the configured line count.

Demo

https://github.com/zed-industries/zed/assets/1185253/e78d4077-5bd5-4d72-a806-67695698af5d

https://github.com/zed-industries/zed/assets/1185253/0b086ec9-eb90-40a2-9009-844a215e6378

[bdsqqq]

very nice

[maxdeviant]

Added two new actions: editor::MoveUpByLines and editor::MoveDownByLines that move the cursor up by the configured line count. Default binding is alt-up and alt-down with 3 lines.

Don’t we already have actions bound to alt-up and alt-down?

I have them bound to moving single lines up and down, but I think by default they’re bound to Tree-sitter syntax selections.

[mrnugget]

Don’t we already have actions bound to alt-up and alt-down?

Yup, sorry! Forgot to update that part of the PR description. I changed it in the code. Will fix PR description now.

[mrnugget]

@maxbrunsfeld what do you think about this?