Add structured filters to pydeephaven

[devinrsmith]

It would be nice to be able to create structured filters from pydeephaven; aiming for an interface that looks something like the server side deephaven.filters would likely be best. or_, and_, not_, is_null, is_not_null should all be easily doable via the respective table.proto Condition message types.

We may want to introduce a new Condition message to fully encapsulate the functionality currently present in pattern; while we have MatchesCondition and ContainsCondition, they are specializations of pattern.

For reference, here is how they map:

    @Override
    public WhereFilter onContains(Reference reference, String searchString, CaseSensitivity caseSensitivity,
            MatchType matchType) {
        final int flags = caseSensitivity == CaseSensitivity.IGNORE_CASE ? Pattern.CASE_INSENSITIVE : 0;
        return WhereFilter.of(FilterPattern.of(
                ColumnName.of(reference.getColumnName()),
                Pattern.compile(Pattern.quote(searchString), flags),
                Mode.FIND,
                matchType == MatchType.INVERTED));
    }

    @Override
    public WhereFilter onMatches(Reference reference, String regex, CaseSensitivity caseSensitivity,
            MatchType matchType) {
        final int flags =
                (caseSensitivity == CaseSensitivity.IGNORE_CASE ? Pattern.CASE_INSENSITIVE : 0) | Pattern.DOTALL;
        return WhereFilter.of(FilterPattern.of(
                ColumnName.of(reference.getColumnName()),
                Pattern.compile(regex, flags),
                Mode.MATCHES,
                matchType == MatchType.INVERTED));
    }