Fix crash on child frame creation (bug#65817)

Fix crash on child frame creation (bug#65817)

* src/nsterm.m ([EmacsView initFrameFromEmacs:]): Reorder the way the
frame and layers are created.
([EmacsView makeBackingLayer]): Change to the newly renamed method
below.
([EmacsLayer initWithColorSpace:doubleBuffered:]):
([EmacsLayer initWithDoubleBuffered:]): Rename the method and remove
the colorspace argument as it's no longer able to be set on initial
creation.
* src/nsterm.h: Use new method prototype.