Page up/down and half up/down consistency

[EpocSquadron]

If it intent is to be consistent with the keybindings for screen movement from vim, we should ensure they are in place and act consistently throughout:

• Add ctrl-f and ctrl-b as equivalents of page down and page up in normal mode
• Implement ctrl-d and ctrl-u for popups
• Implement ctrl-d and ctrl-u for pickers
• Add ctrl-f and ctrl-b to popups, to complement the half height equivalents

[sudormrfbin]

• Add ctrl-f and ctrl-d as equivalents of page down and page up in normal mode

We already have ctrl-f, ctrl-b, ctrl-d and ctrl-u in normal mode:

helix/helix-term/src/keymap.rs

Lines 628 to 631 in 392dfa0

	"C-b" | "pageup" => page_up,
	"C-f" | "pagedown" => page_down,
	"C-u" => half_page_up,
	"C-d" => half_page_down,

[EpocSquadron]

Somehow missed that.

[EpocSquadron]

#1612 will fix the third task, and leave the half-height equivalents for another PR.

[EpocSquadron]

Updated for accuracy. We just have a few places to implement the half-page movements and then this is all set.

[Rudxain]

Is there a chance that some future release will have a j/k equivalent for doc popups? I like the half-page movement, but sometimes it's convenient to have fine-grained per-line movement