Rewrite construct_context.sh in Python.

This allows to reuse SDK version comparison routine from other Python
scripts. With the addition of non-numeric versions comparison has become
more complex, and the deleted shell script did it incorrectly: it used
comparisons like `[[ "S" -lt 28 ]]` which results in "true" as strings
are converted to zero in numeric context. This resulted in adding legacy
libraries to class loader context of apps targeting recent SDK versions.
The error was masked because currently there is only one non-AOSP app
that uses the script (GoogleDialer), and it targets numeric SDK version.

Test: lunch aosp_cf_x86_phone-userdebug && m
Bug: 132357300
Change-Id: I26e752e29b5453fd3e29d5dbfbe4d9df9c0a55b7