Update JDT to support Java 17 language features

[Colin Alworth]

In earlier testing, JDT 3.27.50 was the first version that had all Java 17 features - we used a beta release for this work. We should update to the latest stable JDT, in an attempt to also resolve bugs found in testing since that version was released.

Likely will also require updating asm.

This ticket will also include testing for the Java 12-17 language features that do not require changes to GWT. This probably includes:

• Java 15 text blocks https://openjdk.org/jeps/378
• Java 17 sealed classes https://openjdk.org/jeps/409

If any of those need GWT changes, we'll pull it out into its own ticket.