feat(sbb-checkbox, sbb-radio-button): split into regular and panel variants

[MarioCastigliano]

Closes #2395

BREAKING CHANGE: sbb-selection-panel has been renamed to sbb-selection-expansion-panel. The sbb-checkbox and sbb-radio-button components cannot be used anymore with sbb-selection-expansion-panel (does not apply for cases where they are slotted inside the content slot). As a replacement, we introduce the new components sbb-checkbox-panel and sbb-radio-button-panel, which could also be used standalone in cases where there is no content. sbb-checkbox-group and sbb-radio-button-group also support the panel variants.
How to migrate?

• Rename usages of sbb-selection-panel to sbb-selection-expansion-panel.
• Inside the sbb-selection-expansion-panel, replace sbb-checkbox with sbb-checkbox-panel and sbb-radio-button with sbb-radio-button-panel (does not apply for cases where they are slotted inside the content slot of the sbb-selection-expansion-panel)
• In cases where there was no content (slot), don't use sbb-selection-panel/sbb-selection-expansion-panel anymore, but directly use sbb-checkbox-panel or sbb-radio-button-panel.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 93.15068% with 5 lines in your changes are missing coverage. Please review.

Project coverage is 93.13%. Comparing base (e6397df) to head (f397699).
Report is 52 commits behind head on main.

Files	Patch %	Lines
...io-button/radio-button-group/radio-button-group.ts	81.81%	4 Missing ⚠️
...mponents/checkbox/checkbox-group/checkbox-group.ts	94.44%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2552      +/-   ##
==========================================
- Coverage   93.18%   93.13%   -0.06%     
==========================================
  Files         316      315       -1     
  Lines       25389    24804     -585     
  Branches     2063     2013      -50     
==========================================
- Hits        23660    23100     -560     
+ Misses       1696     1671      -25     
  Partials       33       33              

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