Resolve GrantsForUser queries via resolveQuery()

[dkanney]

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For each grantsForUser repo function, the logic to map from DB object -> perms.GrantTuple was very similar.

• This PR reduces code by removing those functions & moves the mapping logic into GrantsForUser
• Created a new function, resolveQuery(), to determine which query to use based on the request scope & the resources' applicable scopes