Allow failed matcher results to be tagged as errors

Some Matchers typecheck for specific types that they know how to handle. Currently, they return false if it is not one of the expected types. This leads to undesirable behavior. For example, the following passes:
`expect(123, isNot(contains(2));`

It would be better for contains to throw when it receives anything other than an expected type. From what I can find, the other matchers that have this behavior are
- everyElement
- everything in string_matchers.dart
- everything in numeric_matchers.dart

Start with contains and everyElement, then inspect string_matchers.dart and numeric_matchers.dart for matchers that return false after receiving an unsupported type. Trace the existing matcher result handling and tests to determine how failed results should be tagged as errors. Done means unsupported-type inputs no longer pass through negated matchers as ordinary mismatches.

Written by the indexing model from the issue text.