Make template engines more robust for uses like freemarker and velocity portlets

• Type: Story
• Status: Closed
• Priority: Minor
• Resolution: Completed
• Affects Version/s: None
• Fix Version/s: Master
• Component/s: Portal Services, Portal Services > Templates Engine
• Labels: None
• Git Pull Request: https://github.com/brianchandotcom/liferay-portal/pull/38054

1) Currently the template engines use a very bad pattern for adding TemplateResourceParsers. Change to service oriented design.

2) They rely on the legacy ServletContextPool for getting ServletContexts. However, none of the skinny WAB contexts are available by default through this mechanism. Change to service oriented design.