Allow customization of terminal title

[duncanbeevers]

Summary

Previously, geometry showed output in three locations:

• GEOMETRY_PROMPT
• GEOMETRY_RPROMPT
• GEOMETRY_INFO

This PR adds two new display locations:

• GEOMETRY_TITLE
• GEOMETRY_RUNTITLE

Details

Geometry was already implicitly updating the terminal title.
This PR allows configuration of these locations through the same paradigm as drives the rest of geometry.

The original title-controlling functions; geometry::clear_title, and geometry::set_title ran with an implicit lifecycle.

Challenges

De-coloring

The biggest challenge with this PR was de-coloring the output of geometry plugins.
The deansi function included here is hand-rolled and worked with the handful of functions I tried out; includinggeometry_path,geometry_node, and geometry_hostname.

Limited testing

I've primarily developed/tested this in iTerm. It looks a little funny in Terminal.app

iTerm	Terminal.app

No current command

This PR is a regression, since the currently-executing command is no longer exposed in the terminal title.
It seems simplest to expose it as a generic geometry function, like geometry_cmd or something, but it may only be useful when used in GEOMETRY_RUNTITLE.

[jedahan]

Great idea! I'd be happy to merge with a few minor changes:

• Add this feature to the changelog

• Set the default runtitle to show the currently running command (with or without geometry_cmd as an external function, I am not sure it makes sense externally)

• (optional) Think if there could be a better name for RUNTITLE, where better could mean more consistent with zsh naming of things. For example, CMDTITLE since it is precmd. I am happy to merge as RUNTITLE though.

[duncanbeevers]

@jedahan I pushed a change that adds a geometry_cmd internal function used for displaying the currently-executing / last-executed command.

I didn't find a nice way to restore the " @ " in between the command and PWD, like in the old baked-in term title.
I thought maybe there was a way to do it with geometry_echo.

Any suggestions here would be appreciated.

[jedahan]

I am happy keeping it as is (no " @ ") - geometry::wrap uses GEOMETRY_SEPARATOR, which is more consistent with the other output

[duncanbeevers]

@jedahan I've squashed this down to a single commit and updated the commit message with a summary and explanation of the changes.

[jedahan]

Thanks a bunch @duncanbeevers !