Fixed unexpected configuration change causing activity relaunch

In commit ebcc875f we migrated the setting of the task override
configuration from WM to AM. However, the migration changed the
construction of the override configuration to take in the service
configuration as the starting value. This is incorrect since the
only values that should be set in the override configuration are
the ones that change due to resizing. We now seed the override
configuration with the EMPTY value to make it obvious that the
object should be constructed with the default values.

Also, fixed issue with WM telling activity manager to resize a stack
when the stack is already the size it wants.

Bug: 25776219
Change-Id: I882979aa87b49e7a5dc993bd9223fbd6e6cf6471