[firebase_analytics] add missing named events tracking

[juliocbcotta]

Description

This PR:

• add some named events for firebase analytics.
• updated logShare to require a third parameter.
• update the list of reserved event names.
• include some constants that are in the documentation, but are not used. (yet?)

NOTE: Should a new parameter in the logShare force major version update?

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Breaking Change

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[collinjackson]

Thanks, this looks good. It's a bit unfortunate to do a major version bump for such a small change but I think we should probably stick to semVer here.

[dotdoom]

Please forgive me my ignorance here, but what's the point of marking the new parameter @required and making this a breaking change for all existing users of firebase_analytics?

The Firebase documentation does not talk about required parameters, but I'm interested in learning what drives such strict limitations in Flutter.

[juliocbcotta]

@dotdoom , there is no indication of that parameter as being optional in the documentation neither.

[dotdoom]

The top of the documentation page I mentioned above says that all events (except some google_ presets) are custom and so are parameters. It gives a list of events as a suggestion.

But I am buying ambiguous documentation as a reason, although it's unfortunate that we get to break users every time those suggestions change.