rethink the names of the flag count API methods

Copied from a duplicate issue:

getCounts() plural is appropriate when returning an array of individual counts.

but count/total singular should be used for

getEntityCount(),
getTotal()
getUserCount()

This will clash with the efforts to rename getTotals() but as long a we choose the singular version of that name ..

To summarize, we have 4 methods currently in the count API, which can be briefly described thus:

- get a summary of all the flag counts on a single entity
- get the count of all of a flag's flaggings
- get the count of all of a flag's flagged entities
- get the count of all of a flag's flagged entities for a particular user

Let the bikeshedding begin!

Off the top of my head, I propose:

- get a summary of all the flag counts on a single entity: getEntityCounts
- get the count of all of a flag's flaggings: getFlaggingCount
- get the count of all of a flag's flagged entities: getEntityCount (urgh! one letter away from getEntityCounts! We need something better)
- get the count of all of a flag's flagged entities for a particular user: getUserFlaggingCount

Bit more specific, but more wordy:

- get a summary of all the flag counts on a single entity: getEntityFlagCounts
- get the count of all of a flag's flaggings: getFlagFlaggingCount
- get the count of all of a flag's flagged entities: getFlagEntityCount
- get the count of all of a flag's flagged entities for a particular user: getUserFlaggingCount... but then strictly speaking, this one should be getUserFlagFlaggingCount, no?

#2476499: Give the documentation of the flag count API some love. has been committed to the D8 branch.

I'm going to set this to needs review, since the proposed name changes need review before a patch is made.

> I used getUserFlagFlaggingCount name for getUserCounts method because we didn't change it implementation.

Yup, that makes sense.

Thanks for the patch & the reroll.

Committed, and CR updated.