Fix API in CaptivePortal, StaticIpConfiguration

 - Add documentation to CaptivePortal#logEvent
 - Add paragraph breaks to StaticIpConfiguration class javadoc
 - Format javadoc for API documentation
 - Move setters to a builder and hide fields for apps targeting P or
   older
 - Document StaticIpConfiguration getters and builder setters
 - Add documentation for StaticIpConfiguration#getRoutes

Bug: 129362244
Bug: 129433304
Test: built, flashed, booted, WiFi working
Test: atest FrameworksNetTests NetworkStackTests
Change-Id: Ia66c1097f01ca87d02eba3456547aedb1e480186