Previously, there was no way to traverse the trie structure and no way
to identify specific nodes in the trie. That made it impossible to
analyze the trie structure resulting from loading a set of flags. This
change adds type and selector properties to nodes as well as access to
the child nodes of a node to allow for the structure to be analyzed.
Bug: 202154151
Test: m out/soong/hiddenapi/hiddenapi-flags.csv
atest --host signature_trie_test verify_overlaps_test
pyformat -s 4 --force_quote_type double -i scripts/hiddenapi/signature_trie*
/usr/bin/pylint --rcfile $ANDROID_BUILD_TOP/tools/repohooks/tools/pylintrc scripts/hiddenapi/signature_trie*
Change-Id: Ia4714dbf59f6fd143aa3bf3ad1a59cd073d2175b
92532e72a1