This commit:
* Removes the ability to drag the window by the tab bar. I added
that in anticipation of needing to do custom title bar dragging
with Wayland, but it turned out both to be not required and not
possible to drag windows around in that way.
* Replaces the drag logic with dragging the scrollbar thumb
* Clicking above the scrollbar thumb is equivalent to page up
* Clicking below the scrollbar thumb is equivalent to page down
This commit adds a scrollbar that shows the scroll position but
that does not currently allow dragging to scroll.
The scrollbar occupies the right hand side window padding.
The width of the scrollbar can be set by explicitly configuring
`window_padding.right`. If the right padding is set to 0 (which
is its default value), and the scroll bar is enabled then the cell
width will be used for the right padding value instead.
The scrollbar can be enabled/disabled via this config setting:
```
enable_scroll_bar = true
```
Its color by this:
```
[colors]
scrollbar_thumb = "#444444"
```
(Note that color palette config will be reloaded when the config
file is changed, but you'll need to spawn a new tab/window to
see the effects because we cannot assume that a config reload should
always replace a potentially dynamically adjusted color scheme in
a tab).
This commit adds some plumbing for describing the cursor shape
(block, line, blinking etc) and visibility, and feeds that through
the mux and render layers.
The renderer now knows to omit the cursor when it is not visible.
previously we would only ever copy to the clipboard when the selection
was changed.
Now we respect the Copy keypress and have it re-copy the selection
into the clipboard.
This is a bit of a large commit because it needed some plumbing:
* Change mux creation to allow deferring associating any domains,
and to change the default domain later in the lifetime of the
program
* De-bounce the empty mux detection to allow for transient windows
during early startup
* Implement a bridge between the termwiz client Surface and the
frontend gui renderer so that we can render from termwiz to
the gui.
* Adjust the line editor logic so that the highlight_line method
can change the length of the output. This enables replacing
the input text with placeholders so that we can obscure password
input
