Components: Missing font-size declarations

[mirka]

What problem does this address?

#42747 uncovered that some components rely on a font-size: 13px being set in the surrounding CSS context. This is not a given, and we need that font-size to be explicitly set in each component for them to be self-sufficient.

What is your proposed solution?

This could've been fine if the component library were designed with dynamic sizing in mind, but in reality they are designed with fixed pixel values, and the majority of components do have an explicit font-size: 13px set within them. So let's maintain that consistency throughout the package.

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Can be closed when the following are merged:

• Update control labels to the new uppercase styles #42789
• Tooltip (Experimental), CustomSelectControl, TimePicker: Add missing font sizes styles which were necessary in non-WordPress contexts #42844

[mirka]

We may uncover some minor cases, but the known ones are all addressed now.