chore(implementation): use Jetty-12.1 core without servlets

[lachlan-roberts]

This is based on the work from #235.

Port the invoker to upgrade to Eclipse Jetty-12 version 12. Specifically using the new core APIs of Eclipse Jetty-12 that allow the overhead of a Servlet container to be avoided.

BREAKING CHANGE: use Java 17 or above, as required by Eclipse Jetty-12.

Replaces

• Port to use Jetty-12 core without servlets #235
• chore(implementation): Use Jetty handlers rather than Servlets #241
• chore(deps): Upgrade to Jetty-10 #244

[ludoch]

Thanks!
We need to remove jdk11 constraints in builds. I guess only a Googler can understand and change the kokoro files to jdk17

Also all references with maven.compiler.source>11</maven.compiler.source> need to change to 17

[ludoch]

For ex, remove https://github.com/GoogleCloudPlatform/functions-framework-java/blob/cd6caeda00262b2558815ae22cfc726c0638122a/.github/workflows/buildpack-integration-test.yml#L17https://github.com/GoogleCloudPlatform/functions-framework-java/blob/cd6caeda00262b2558815ae22cfc726c0638122a/.github/workflows/buildpack-integration-test.yml#L17

Maybe add java21 or 25

[ludoch]

@akerekes please help on google internal kokoro workflows.
The entire new code now has to only work with java17,21 and 25, so drop 11 and add new configs.

[akerekes]

Hi @lachlan-roberts , thank you for the PR! I'll work on the Google internal side. One note on the timeline is that Cloud Function deprecates java11 at the end of the month: https://cloud.google.com/functions/docs/runtime-support#java so my preference is to have this PR ready to merge, but wait until the end of the month with the merge, then do it in early November and release a new version of the FF-java library.