Improve translation strings

[rabmalin]

/wp-includes/class-wp-duotone.php L904

__( 'The duotone id "%s" is not registered in theme.json settings' ),

theme.json is never going to be translated in another languages. Would it make more sense if we take that part out of the translation string and use placeholder?

Another case:

"%s" in theme.json settings.color.duotone is not a hex or rgb string.

settings.color.duotone wont be translated I guess.

[Presskopp]

there's one more:

Some of the theme.json settings.spacing.spacingScale values are invalid

[SergeyBiryukov]

In 57135:

I18N: Move code out of translatable strings in a few error messages.

Follow-up to [54272], [56101].

Props rabmalin, Presskopp.
Fixes #59563.