Update language to comply with Android's inclusive language guidance

The binary uses flags to mean both command-line parameter names
and the API names, used in files and internally in the class.

Internal representation and command-line parameter names are updated to
use more inclusive language. However, the output file produced by
`generate_csv` function still uses old flags. Format update in
the input/output files is out of scope for this change
and will be updated in the follow-up changelist.

See https://source.android.com/setup/contribute/respectful-code for
reference.

Bug: 161896447

Test: python3 generate_hiddenapi_lists_test.py

Change-Id: I36c85ce04b89ba3e4eee319f95511110d2c4374e