Update FontManager#getFontConfig to require permission

There is no security risk in getFontConfig without calling permissions
but for keeping compatibility it is recommended to have permissions
to all (non-mainline) system APIs.

To be able to test these APIs, grant UPDATE_FONTS permission to shell.

Bug: 181796732
Test: atest FontManagerTest
Change-Id: Ic1f663e1e01f3625a076e68949f717366e79f5fa