add "goto next workspace diagnostic" commands

[plul]

Helix currently has commands to go to the next LSP diagnostic in the present document, and it has a picker for workspace diagnostics and the ability to show in the status bar the number of workspace errors and warnings, but it lacks a seemingly simple "goto next workspace diagnostic" command.

This PR adds

• goto_next_diag_workspace (any diagnostic level)
• goto_next_error_workspace (errors)
• goto_next_warning_workspace (errors and warnings)

Addition of goto_prev_..., goto_first_... and goto_last_... commands to match the existing ones that only search the current document I think are less important (the ones I personally want are almost always the goto_next_... variants), but should be easy to add as a follow up PR if the structure of this one is accepted.

Discussion of default keybindings for these commands should be reserved for a separate PR.

I'm a first time contributor to Helix, so bear that in mind when reviewing. Some helper functions I wasn't sure in which module to best place them. But any feedback or push back is welcomed.

Some related issues/pull-requests:

• Go to next LSP diagnostic in workspace #3116
• Add goto_next_diag_error/goto_prev_diag_error #3405

[plul]

Rebased and added first variants:

    goto_first_diag_workspace (any diagnostic level)
    goto_first_error_workspace (errors)
    goto_first_warning_workspace (errors and warnings)

[plul]

Rebased on 25.01.1

[plul]

Rebased on master (for the newly merged file picker).

[plul]

For anyone wishing to test this out, you can use the following keybindings as an example:

[keys.normal]
1 = "goto_next_diag_workspace"
2 = "goto_next_warning_workspace"
3 = "goto_next_error_workspace"
C-1 = "goto_first_diag_workspace"
C-2 = "goto_first_warning_workspace"
C-3 = "goto_first_error_workspace"

This is what I've been daily-driving for the past 8 months or so.