Analyzer to warn against accidental usage of AddEntityFrameworkProvider

[roji]

Following #25451, we can warn when AddEntityFrameworkProvider is called from user code instead of AddProvider. Providers would disable this diagnostic.

[ajcvickers]

It is necessary to call these methods from user code when taking control of the internal service provider. Most people should not be doing that, but there are times when it makes sense.

[roji]

@ajcvickers assuming the legitimate cases are rare enough to warrant hiding these methods from Intellisense, it could make sense to also have a diagnostic (which users can suppress). But if you feel this is bad for some reason we can close.