Add `#verified` and `#valid_message?` to MessageVerifier

This commit adds a `#verified` method to
`ActiveSupport::MessageVerifier` which will return either `false` when
it encounters an error or the message. `#verify` continues to raise an
`InvalidSignature` exception on error.

This commit also adds a convenience boolean method on `MessageVerifier`
as a way to check if a message is valid without performing the
decoding.
Silence Minitest for plugin tests.

Fixes https://github.com/rails/rails/issues/17340.

Use Minitest::BacktraceFilter instead of removing all silencers. This
will allow the backtrace for all libraries in the plugin to be shown
while removing noise generated by Minitest's backtrace.
pg tests, get rid of global schema `schema_1`.
no need to pass native_database_types around
Merge pull request #17576 from senny/native_database_types

no need to pass native_database_types around
Allow failures for mysql adapter tests
Merge pull request #17862 from lucasmazza/lm-hide-action

`_generate_paths_by_default` should always be private.
Merge pull request #17867 from tgxworld/silence_minitest_plugins

Silence Minitest for plugin tests.
Merge pull request #17727 from lleger/lleger-add-methods-to-message-verifier

Add new methods to MessageVerifier
Refactor debug view
Avoid logic in ERB and use helpers
Merge pull request #17873 from kirs/refactor-debug-erb

Refactor debug view
Prefer object/nil over `true`/`false`

This is the project guideline and the reasons are:

* That follows standard Ruby semantics.
* Allows the implementation to avoid artificial code like !! or something ? true : false
* You do not need to rely on the exact type of 3rd party code. For
example, if your method returns str.end_with?('foo') you do not need to
make sure end_with? returns a singleton. Your predicate just propagates
predicate semantics up regardless of what end_with? returns.
Allow to unscope where conditions using `arel_table` with Symbol

This commit fixes the following case.

    User.where(User.arel_table[:created_at].lteq(1.year.ago)).unscope(where :created_at)