c/validation: clean up GTest matchers, utilities

- Add test helper to execute a statement and get back `Result` (for DDL)
- Reorganize and document the quirks
- Add test helper to execute a statement and get back a single batch (tests assume they will always be a single batch but that isn't necessarily true)
- Create or use utilities for iterating over streams (https://github.com/apache/arrow-nanoarrow/issues/403)
- Create utilities for asserting on values, preferably using native C++ types for clarity, and so that we can use the native GTest matchers
- Remove the StreamReader class
- Consolidate the Handle class
- Create utilities for asserting on schemas more effectively (particularly for parameterized/nested types). Possibly something like the standard GTest ElementsAre.