Allow Shift+b to blink backwards

[pllim]

Description

This pull request is to add the ability to press Shift + b to blink backwards.

Fixes #1424

TODO

• Do we also want to remove blink button from toolbar and make it an actual plugin so user can do blink backward, forward, or even auto blink on timer? Or is that out of scope here? No, right-click to blink backwards when tool is active works for now.
• Do we want to future proof by having blink to ignore viewer load order but instead accept a list of data labels in arbitrary order that user can customize? This would allow user to reorder the blink order or is that out of scope here? Also see Imviz: Reorder layers #747 -- Let's defer as future work, as that issue impacts more than just blinking.

Checklist for package maintainer(s)

This checklist is meant to remind the package maintainer(s) who will review this pull request of some common things to look for. This list is not exhaustive.

• Are two approvals required? Branch protection rule does not check for the second approval. If a second approval is not necessary, please apply the trivial label.
• Do the proposed changes actually accomplish desired goals? Also manually run the affected example notebooks, if necessary.
• Do the proposed changes follow the STScI Style Guides?
• Are tests added/updated as required? If so, do they follow the STScI Style Guides?
• Are docs added/updated as required? If so, do they follow the STScI Style Guides?
• Did the CI pass? If not, are the failures related?
• Is a change log needed? If yes, is it added to CHANGES.rst?
• Is a milestone set?
• After merge, any internal documentations need updating (e.g., JIRA, Innerspace)?

[codecov]

Codecov Report

Merging #1558 (a3a6518) into main (207f7a3) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1558   +/-   ##
=======================================
  Coverage   85.44%   85.45%           
=======================================
  Files          94       94           
  Lines        9058     9061    +3     
=======================================
+ Hits         7740     7743    +3     
  Misses       1318     1318           

Impacted Files	Coverage Δ
jdaviz/configs/imviz/plugins/tools.py	84.49% <100.00%> (ø)
jdaviz/configs/imviz/plugins/viewers.py	83.14% <100.00%> (+0.28%)	⬆️

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[kecnry]

I think having the tool in the toolbar is convenient, and that adding reversed functionality does not quite warrant the "overhead" of a full plugin (yet). Maybe just adding a note of the shift+B to the existing tool's tooltip would help make this a bit more discoverable? It might also be possible to have a right-click with the tool active to trigger reversed blink?

[kecnry]

I added a commit that implements support for right-click. Note that tool is still activated with a left click, but then right-clicking on the viewer blinks in the reversed direction.

[hcferguson]

Looks good and works like a charm for me with both B and the right click!

[pllim]

Harry's approval counts as second approval? 😸