Issue 59778/font family control error

[zeopix]

What?

Fixes error that breaks the block where the FontFamilyControl is used without fontFamilies specified. It now returns an array with custom and theme font families if present.

Why?

A Font Family selector without specifying fonts was a working feature and has been broken recently with the changes in the value of the fontFamily setting. - Issue 59778

How?

It just need an adjustment to merge custom fonts and theme fonts when selecting the setting.

Testing Instructions

1. Use a block that makes use of FontFamilyControl without specifying fontFamily, such as LanguageSwitcher from WPML, to take advantage of theme and custom fonts.
2. Add the block, click on "Font Family" control in the sidebar Block section.
3. Notice the block displays the current theme preconfigured fonts.
4. Add a custom font into the theme (Site Editor > Styles > Typography > Install Font).
5. Go to the block editor, check the new font is available.
6. Choose an old theme, like twenty-nineteen.
7. Go to block, notice the section is empty, but block is not broken as before.

Testing Instructions for Keyboard

-no ui changes-

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[github-actions]

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[t-hamano]

Hi @zeopix,

Sorry for the late review.

The data obtained via useSettings may include three origins: default, theme, and custom. Therefore, we need to consider not only theme and custom, but also default.

I suggest reusing the logic of the mergeOrigins function and changing it as follows.

if ( ! fontFamilies ) {
	fontFamilies = [ 'default', 'theme', 'custom' ].flatMap(
		( key ) => blockLevelFontFamilies[ key ] ?? []
	);
}

Note: You may want to use the mergeOrigins() function itself, but that is not recommended. See the discussion starting with this comment for why.

Also, I would be happy if you could rebase this PR using the latest trunk.