Update docs for custom logo functions

[sabernhardt]

In #37011, I missed that the get_custom_logo() function summary and @since note were not updated when removing the link became optional.

The summary also would need to be updated for the_custom_logo.

[sabernhardt]

51075.patch​ is a first draft. I'm sure the wording can be clearer, though.

[SergeyBiryukov]

In 48832:

Docs: Update documentation for get_custom_logo() and the_custom_logo() to mention the unlink-homepage-logo theme feature.

Follow-up to [48039], [48283], [48749], [48757], [48758].

Props sabernhardt.
Fixes #51075.

[SergeyBiryukov]

In 48833:

Docs: Update documentation for get_custom_logo() and the_custom_logo() to mention the unlink-homepage-logo theme feature.

Follow-up to [48039], [48283], [48749], [48757], [48758].

Props sabernhardt.
Merges [48832] to the 5.5 branch.
Fixes #51075.

[joyously]

I was answering a forum question about this, and noticed that the add_theme_support function does not mention the unlink-homepage-logo feature.

[SergeyBiryukov]

Replying to joyously:

I was answering a forum question about this, and noticed that the add_theme_support function does not mention the unlink-homepage-logo feature.

Thanks for flagging that! unlink-homepage-logo is not a feature by itself, it's one of the values for the custom-logo feature, same as width, height, flex-width, flex-height, and header-text.

It was mentioned in a @since note for 5.5.0, see [48749]:

@since 5.5.0 The `custom-logo` feature now also accepts 'unlink-homepage-logo'.

That said, the documentation for the ​Custom Logo feature did indeed miss it. I've updated that section to include unlink-homepage-logo.

[SergeyBiryukov]

In 50912:

Docs: Clarify the @since note for unlink-homepage-logo in get_custom_logo().

This should make it clearer that the value applies to the custom-logo theme feature.

Follow-up to [48039], [48283], [48749], [48757], [48758], [48832].

Props joyously.
See #51075, #52628.