raise error for sidecar or popout when not supported

[kecnry]

Description

This pull request raises an error when trying to show a widget in popout or sidecar when they are not supported (i.e. in VS Code). Related to #3251.

Change log entry

• Is a change log needed? If yes, is it added to CHANGES.rst? If you want to avoid merge conflicts,
  list the proposed change log here for review and add to CHANGES.rst before merge. If no, maintainer
  should add a no-changelog-entry-needed label.

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 milestone set? Set this to bugfix milestone if this is a bug fix and needs to be released ASAP; otherwise, set this to the next major release milestone. Bugfix milestone also needs an accompanying backport label.
• After merge, any internal documentations need updating (e.g., JIRA, Innerspace)?

[kecnry]

@mariobuikhuizen - is this sufficient, or would accessing getBaseUrl() be more appropriate (in which case can that be exposed back to python in ipypopout)?

[mariobuikhuizen]

I don't think there is a 1 on 1 mapping of where ipypopout and sidecar work. I think sidecar has different requirements than ipypopout.

[kecnry]

do you have any suggestions on which conditions to use for each for now then?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.81%. Comparing base (88d82f9) to head (a9473d6).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3309   +/-   ##
=======================================
  Coverage   88.81%   88.81%           
=======================================
  Files         125      125           
  Lines       19036    19037    +1     
=======================================
+ Hits        16906    16907    +1     
  Misses       2130     2130           

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