JIT: update byref null check logic to handle field chains (#23850)

JIT: update byref null check logic to handle field chains (#23850)

The jit was not properly accumulating offsets when figuring out if a byref
should be null checked.

Use a non-null MorphAddressContext as indication that GT_FIELD and GT_IND
nodes are actually part of an ongoing address computation.

During field morphing propagate the current address context to the child node,
instead of starting a new one.

Fixes #23791.