[erl-frontend] Validate association kind in map pattern
[erl-frontend] Validate association kind in map pattern

Summary: Associations in map patterns should only be exact (`:=`). We did not validate this previously (D28832961 (https://github.com/facebook/infer/commit/65884018dc04093173ed2d741354650609eea593)), because we didn't have certain AST transformation passes that would eliminate some special functions that allowed invalid association kinds (later removed by transformation). However, with D29103633 (https://github.com/facebook/infer/commit/25711189a8a62adb2c30d5b625e56bd734d079fc), we get the AST from a different source and these invalid cases are removed, so the check is added.

Reviewed By: mmarescotti

Differential Revision: D29162325

fbshipit-source-id: a47d9f05d

jvillard/infer,facebook/infer,jvillard/infer,jvillard/infer,jvillard/infer,jvillard/infer,facebook/infer,facebook/infer,jvillard/infer,facebook/infer,facebook/infer,facebook/infer,facebook/infer,jvillard/infer