Enable supportsEnterPipOnTaskSwitch early on

We need to enable supportsEnterPipOnTaskSwitch
before we check for the PiP state to be valid in PiP2.

This should fix the CTS test case where we launch the
TestActivity over a pip-able PipActivity with auto-enter flag on.

Bug: 359675378
Flag: com.android.wm.shell.enable_pip2_implementation
Test: atest PinnedStackTests#testAutoPipOnLaunchingRegularActivity
Change-Id: I75e68e0bbbbb7a1bfd965684fb666f21f8d27d8d