Removing Tab key for mode switching ignored the use this key in other contexts.

• Node grope editing (NLA_OT_tweakmode_enter/exit).
• Metastrip editing (SEQUENCER_OT_meta_toggle).
• Action channels edit toggle (ANIM_OT_channels_editable_toggle).
• NLA edit toggle (NLA_OT_tweakmode_enter/exit).

Generally, I think it's useful to have a key that enters into the selection to edit it's content at a more fine-grained level.

T55162 ignores this aspect of the keymap, further, I don't think using numbers keys for these cases works very nicely.

This patch:

• Reinstates Tab for toggling editmode.
• Uses number keys for other modes (since this was indeed not working well).
• Sets search to ~ (accent-grave key).
• Sets mode vertex/edge/face mode switching to shift-tab.

Pros

• Tab is always used for editing in different contexts, increasing consistency.

Cons

• Two keys are used for the same thing (2 key and tab).

Other Notes

• Edit-mode remains accessible from number key and tab, this is done so the associated number key matches the menu order.
• Keyboards without the ~ key will use the physical key to the left of 1 will be used.