bootstat: Allow regex matches for boot reasons

If the matching string contains a [, \ or *, then it is also checked
with a regex match.  Exact match is always tried firsts.  If we do
not find an exact string match, switch to iterate through the entire
list for regex strings to find a match.

This allows us to scale with details without consuming a large
number of enums, permitting details that we do not necessarily want
resolution on to propagate to TRON.  The hierarchical nature of the
boot reason <reason>,<subreason>,<detail>... can cause scenarios
where the <detail> does not matter to TRON, but does matter to
bugreport collection.

Add a bootstat --boot_reason_enum function to expose and test the
kBootReasonMap matchihg algorithm.

Add a kBootReasonMap test that exhaustively tests all built-in
entries, and an example of one regex entry.  New regex entries added
to bootstat.cpp will need a series of exact match examples added into
filter_kBootReasonMap() function.

Test: boot_reason_test.sh kBootReasonMap (or all tests)
Bug: 116838876
Bug: 128929506
Change-Id: I3f7b5de22f99195b7ce99672a212174365960b3f