Create DE_sys APEX data directories.

This creates the directory /data/misc/apexdata, at the same time as other
directories under /data/misc. Then, when apexd has finished activating
APEXes, a directory is created under /data/misc/apexdata for every
APEX, with the same name as the APEX module name.

See go/apex-data-directories.

APEXes are discovered by scanning the /apex directory. It may be better
to delegate this process to a library, but it is proposed to defer that
change to a future CL.

Bug: 141148175
Test: Built and flashed, checked directories were created.
Change-Id: I639d6f490ae0b97f116ce38ff3ac348bd73aa20e