Add more details in the javadocs for new visibility apis.

- Describe the expected behaviour when calling setVisibilityPublic and
setVisibilityRestricted on {MediaRoute2Info.Builder}.

Bug: 266564463
Test: NA as it's just changes in javadocs.
Change-Id: I2bd699b9cfbb8973770898e54f4db7645af3d99b
1 file changed