Plumb pid to Layer Metadata during Layer creation

For shared timeline visualization, the pid of the process owning the
layer is needed to show the information in the respective process
tracks. This change adds pid to the layer metadata that is passed around
during the creation of a layer.

Bug: 170911969
Test: pid section of `adb shell dumpsys SurfaceFlinger --frametimeline -<all/jank>`

Change-Id: Ibd16bf7740d0c1be07cdbd300a1741cfcb6d2ad8