algoliasearch-helper is vulnerable to Prototype Pollution in _merge()

Versions of the package algoliasearch-helper from 2.0.0-rc1 and before 3.11.2 are vulnerable to Prototype Pollution in the _merge() function in merge.js, which allows constructor.prototype to be written even though doing so throws an error. In the "extreme edge-case" that the resulting error is caught, code injected into the user-supplied search parameter may be exeucted.

This is related to but distinct from the issue reported in [CVE-2021-23433](https://security.snyk.io/vuln/SNYK-JS-ALGOLIASEARCHHELPER-1570421).

**NOTE:** This vulnerability is not exploitable in the default configuration of InstantSearch since searchParameters are not modifiable by users.