fix(vi): enter visual mode through command

[matystroia]

Problem:

Entering visual mode does not actually select char/grapheme under cursor. Thus you have to do something like vlh to actually move selection to cursor. This happens because the parser eats the v input and sets mode manually instead of it going through the usual Command -> EditCommand pipeline.

Solution:

• Add EditCommand::SelectChar that sets selection anchor to current cursor position
• Add Command::EnterViVisual that maps to EditCommand::SelectChar

Mode change still happens in parser, but now through the return value of changes_mode.

[kronberger-droid]

One behavior shift worth knowing about is that the old v path emitted ReedlineEvent::Esc, which closed any open menus. The new path skips that, could you preserve it by changing Command::EnterViVisual mapping:

Self::EnterViVisual => vec![
    ReedlineOption::Event(ReedlineEvent::Esc),
    ReedlineOption::Edit(EditCommand::SelectChar),
],

Also a couple of test before merge?

• Editor-level: EditCommand::SelectChar sets selection_anchor
• End-to-end: v then U on a fresh buffer capitalizes the grapheme under the cursor etc.

Also the EditCommand::SelectChar has a trailing comma.

Afterwards I am fine with landing it.