The issue here was that we'd try to match this:
```
key_event RawKeyEvent { key: Char('t'), modifiers: ALT | LEFT_ALT, phys_code: Some(T), raw_code: 17, repeat_count: 1, key_is_down: true, handled: Handled(false) }
```
which has mods=`ALT|LEFT_ALT` against `ALT` and would fail.
We need to strip out the positional ALTs from the modifiers
in order to successfully match.
refs: https://github.com/wez/wezterm/issues/1958
The copy overlay now has a notion of running in search mode vs. copy
mode; it can be launched in either mode.
Search mode has a separate key table called `search_mode`.
Activating copy mode while search mode is active will now update
the mode of the existing overlay, rather than cancelling and creating
a new instance, and vice versa.
Activating copy mode while search mode is active will replace the
current key table activation (which is assumed to be `copy_mode`)
with `search_mode`, and vice versa.
The viewport is no longer scrolled to the bottom when activating search
mode.
refs: https://github.com/wez/wezterm/issues/993
refs: https://github.com/wez/wezterm/issues/1592
Moves the key handling in the copy overlay to be driven entirely
by configurable key assignments.
Note: copy mode wants you to use the `Copy` assignment to actually
do the copy, but this implementation hides the normal key assignments
by activating the copy mode key table. This will be addressed
in the following commit.
refs: https://github.com/wez/wezterm/issues/993
Create a list of command definitions to hold the default key
assignments.
That list has more metadata, such as a brief and longer human
readable description of the purpose, and allows for (in the
future) reasoning about the context where the command is valid,
as well as providing more information when rendering in the
launcher menu.
refs: https://github.com/wez/wezterm/issues/1485
