Add strip_switch_pad themeable

[has2k1]

Previously, with strip_placement="outside" and a positioned axis sharing the strip's side, the strip sat flush against the axis with no gap. This adds new themeables strip_switch_pad_x, strip_switch_pad_y, and the parent strip_switch_pad (points).

The Axis title/text margins on both sides have also been restored.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.34%. Comparing base (3f63b24) to head (ea1b4fd).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1093      +/-   ##
==========================================
+ Coverage   87.29%   87.34%   +0.05%     
==========================================
  Files         208      208              
  Lines       14602    14660      +58     
  Branches     1825     1827       +2     
==========================================
+ Hits        12747    12805      +58     
  Misses       1282     1282              
  Partials      573      573              

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