useSetting( 'color' ) does not consider deprecated flag

[oandregal]

Description

useSetting allows consumers to access data coming from theme.json. For a few cases, we introduced logic to fallback to the corresponding deprecated setting (see), so userSetting( 'color.custom' ) will fallback to settings.disableCustomColors or typography.lineHeight will fallback to settings.enableCustomLineHeight.

While this works when accessing the setting directly, it doesn't when the consumer accesses the top-level key: useSetting( 'color' ) does not consider the special handling for color.custom and so on.

[jorgefilipecosta]

I'm not sure if we should fix this issue. useSetting('color') should not be used unless one really wants the raw value as they are in the structure. On #36841 I missed the fact that in one of the usages we need the back-compatibility and that was the issue.

[oandregal]

I don't have strong opinions other than fixing the current status, which is bug-prone. Both options (adding the backcompatibility logic or don't allow using color directly) work for me.

[oandregal]

For the record, @youknowriad also argued that we shouldn't allow using useSetting with top-level keys: #36900 (comment)