R1:382e2c32fc10

When an invalid "constraints" parameter is provided to a "*.search" method, raise a more tailored error

Summary:
See <https://discourse.phabricator-community.org/t/constraints-parameter-type-handling-in-maniphest-search/2636>.

(The caller provided `constraints={...}` via cURL, but you can't mix JSON and HTTP parameters like that.)

Test Plan: Called `curl 'http://local.phacility.com/api/maniphest.search?api.token=...&constraints=X'` (with a valid API token), got a more sensible error.

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