Move the creation of the root structure to build/core/main.mk

Since Soong currently doesn't support the `install_directory`
functionality, `system/core/rootdir/Android.mk` cannot be directly
converted to Android.bp. Moreover, its main content is to create
directories and symlinks for the root file system. Therefore, we'll
first rename it and move it to build/core/main.mk for handling.

In addition, consolidate the handling of meta-lic related parts into
`build/core/tasks/meta-lic.mk`.

Bug: 353642907
Test: m -j init.environ.rc
Change-Id: Ie8f8bcae5752d22c331b33a33981a959410f0a69