Auto merge of #14794 - mrnayak:hsts-refactor, r=emilio

Refactor HSTSList to use HashMap

Refactored HSTSList to use HashMap, where the key of HashMap is the base domain. Every time when we check if a host is secure, we find the base domain of the host and get a vector of HSTS entries associated with the base domain.

While this will not give O(1) look up time, we would have a smaller list to iterate for every lookup. I have added one unit test to validate `HashMap` changes.

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