The BaseResource implementation in TypeScript had (and continues to

have) a number of issues. A lot of this stems from just bad design

decisions that were made before we even thought too much about typing or

polymorphism, but some of it is just mistakes or poor understanding of

TypeScript when I first converted it.
This change does the following:

Switches the order of TOptions and TExtraOptions. I had followed

   what Backbone.Model did, but didn't realize that the spina

BaseModel swaps them. This was making it so our call to

CombinedModelConstructorOptions was creating errors.
Adds a base resource data interface, and extends that for subclasses

   that currently define the resource data structure.
Moved payloadFileKeys into the BaseResource implementation. This

   was currently only defined in FileAttachment, but it's used inside

   of BaseResource and by other (not-yet-typescriptified) subclasses.
Changed validate to take in a Partial<TDefaults> instead of

TDefaults, which matches our usage of this method.
Added type labels for everything that's in prototypeAttrs as

   instance members too. This shuts up the type checker about these

   magical properties.
Properly passed in the attributes type for DraftReview.
Added some missing type labels.

Changes 1 & 2 are technically breaking, but the only class that was

affected was ReviewRequest, and it seems highly unlikely that any

third-party code is using this yet, so I want to do it now.
What this doesn't fix is our decision to override fetch, save, and

destroy with incompatible signatures. I'm still puzzling over what to

do there to make it so we don't get huge horrible warnings about any

resource class not being compatible with Backbone.Model.

Ran js-tests.