Update to Jetty 12

[tfmorris]

Jetty 11 implements the Jakarta Servlet 5 API which uses different package naming, requiring changes to Butterfly to support.

It would make sense to bundle some other breaking changes in with this such as an upgrade to Velocity 2.

[Abbe98]

Maybe it would be worth merging all the current pull requests and make a new breaking release? From my perspective the all benefits motivates the breaking changes.

[tfmorris]

Jetty 12 actually supports multiple environments simultaneously:

• EE8 (Servlet 4.0) in the java.* namespace,
• EE9 (Servlet 5.0) in the jakarta.* namespace with deprecated features
• EE10 (Servlet 6.0) in the jakarta.* namespace without deprecated features.
• Core environments with no Servlet support or overhead.

so we actually wouldn't necessarily have to adopt the new package names.

Do folks think we should stick with EE8 or target one of EE9 or EE10?

[tfmorris]

@wetneb expressed an opinion on the linked PR that we should go for Jetty 12 with EE8 (Servlet 4.0).

Any other opinions?

Although the Velocity 2 change is nominally major, there are a bunch of compatibility flags, all of which we've enabled, so it may not actually have an impact on extensions.

The other nominally breaking changes are also likely to have low/no impact.