Utilize Users_Orgs mapping table to do in memory reault filtering

• Type: Feature Request
• Status: Under Review
• Priority: Minor
• Resolution: Unresolved
• Affects Version/s: 6.2.0 CE M3
• Fix Version/s: 6.2.0 CE M3
• Component/s: Core Infrastructure, Performance
• Labels: None
• Git Pull Request: https://github.com/brianchandotcom/liferay-portal/pull/8033

For this particular usage, base on the fact that user normally belongs to very limited number of organizations. The user to org mapping result is cachable without causing a notable memory occupation.
I optimized the user to org sql filtering query in OrganizationLocalServiceImpl to be full mapping query without filter, then process the result in memory. The full mapping query is cached at persistence layer, most likely after warm up won't fire out a db query, and the organization data set per user is very small, process in memory is very efficient.

This solution will add a slight overhead on portal side, but reduce quite a lot database activity. In most cases, the net output should be an improvement.