Don't coerce types in JSON body
Don't coerce types in JSON body

We need to coerce from string when processing multipart/form-data and
urlencoded posts, but should resist the temptation to guess when processing
JSON posts. Reasons in favor of being strict for JSON:

- We want users to send JSON requests conforming to the documented schema.
  Trying to fix up some classes of errors & not others would be confusing.
- Our type coercion currently only applies to top-level properties. In a JSON
  POST, this having this coercion only happen at the top level would be fairly
  confusing for users.
- Running the coercion on large JSON bodies adds unnecessary overhead.

Task: https://phabricator.wikimedia.org/T118470

wikimedia/restbase,eevans/restbase,d00rman/restbase,cscott/restbase,Pchelolo/restbase,gwicke/restbase,inverno/restbase,gwicke/restbase,cscott/restbase,wikimedia/hyperswitch,milimetric/restbase,wikimedia/mediawiki-services-restbase,inverno/restbase,eevans/restbase,wikimedia/restbase,d00rman/restbase,Pchelolo/restbase,milimetric/restbase,wikimedia/mediawiki-services-restbase