MAINT: minor positioner ui tweaks

[ZLLentz]

Description

• Replace the "disabled" broken setpoint widget with a simple bitmask clicker
• Tweak the positioner layouts to enable them to be expandable

Motivation and Context

• I went through all the options for disabled/DISP and this one looked the least bad
• Minor tweaks based on things I noticed while implementing ENH: positioner row widget sizing usability fixes and tweaks typhos#611

The other option that sort of worked for the disabled widget was simple text entry but:

• This had the unit attached (0mm is off, 1mm is on...)
• It was awkward to know to type 0 or 1

I couldn't get typhos to assign a custom enum combobox to this widget. There was an option to have two vertical buttons to click but I didn't like it.

How Has This Been Tested?

Interactively only

Where Has This Been Documented?

Here only, I need to make pre-release notes

Screenshots (if appropriate):

Old "disabled" widget (completely inoperable):

New "disabled" widget:

New widget when disabled (click the right-hand bitmask widget to toggle):

Pre-merge checklist

• Code works interactively
• Code contains descriptive docstrings, including context and API
• New/changed functions and methods are covered in the test suite where possible
• Test suite passes locally
• Test suite passes on GitHub Actions
• Ran docs/pre-release-notes.sh and created a pre-release documentation page
• Pre-release docs include context, functional descriptions, and contributors as appropriate

[tangkong]

Needs another merge commit, but aside from that I'm 👍 on this