Refactor Dialect_Flag

[AdRiley]

Pull Request Description

This combines 3 different styles of flagging into a new single style.

It replaces:

• The old Dialect_flags like use_builtin_bankers
• Test flags like supports_case_sensitive_columns
• Method flags like supports_separate_nan

I haven't replaced them all yet, this adds the framework future MRs will finish the cleanup.

I think in future any test that relies on a flagged behaviour needs to test both sides of that behaviour.

Important Notes

Checklist

Please ensure that the following checklist has been satisfied before submitting the PR:

• The documentation has been updated, if necessary.
• Screenshots/screencasts have been attached, if there are any visual changes. For interactive or animated visual changes, a screencast is preferred.
• All code follows the
  Scala,
  Java,
  TypeScript,
  and
  Rust
  style guides. In case you are using a language not listed above, follow the Rust style guide.
• Unit tests have been written where possible.

[GregoryTravis]

I think this approach is much more readble. I'm inclined to call it something like 'dialect flag' rather than 'property', because 'property' is more vague, and 'dialect flag' indicates clearly that they are set for each dialect.

[radeusgd]

Not 100% convinced, but I have nothing against the change.

[GregoryTravis]

I like this approach because it keeps all the flags together. If each flag were a separate method, they might get separated or out of order, which just makes it more tiring to add or change one across all the backends.