Add JDK 20 in package.json

[mavaddat]

Fixes #3023

JDK 20

This release is the Reference Implementation of version 20 of the Java SE Platform, as specified by JSR 395 in the Java Community Process.

JDK 20 reached General Availability on 21 March 2023. Production-ready binaries under the GPL are available from Oracle; binaries from other vendors will follow shortly.

The features and schedule of this release were proposed and tracked via the JEP Process, as amended by the JEP 2.0 proposal. The release was produced using the JDK Release Process (JEP 3).

Features

429:	Scoped Values (Incubator)
432:	Record Patterns (Second Preview)
433:	Pattern Matching for switch (Fourth Preview)
434:	Foreign Function & Memory API (Second Preview)
436:	Virtual Threads (Second Preview)
437:	Structured Concurrency (Second Incubator)
438:	Vector API (Fifth Incubator)

Schedule

2022/12/08		Rampdown Phase One (fork from main line)
2023/01/19		Rampdown Phase Two
2023/02/09		Initial Release Candidate
2023/02/23		Final Release Candidate
2023/03/21		General Availability

[fbricon]

This PR can only be merged once the server side supports Java 20

[mavaddat]

This PR can only be merged once the server side supports Java 20

Ah yes, that makes sense. How soon do you expect the Language Server would support JDK 20?

[snjeza]

@mavaddat

• https://github.com/redhat-developer/vscode-java/blob/master/README.md#features

Could you, please, replace

* Supports code from Java 1.5 to Java 19

with

* Supports code from Java 1.5 to Java 20

[snjeza]

How soon do you expect the Language Server would support JDK 20?

@mavaddat you may want to take a look at eclipse-jdtls/eclipse.jdt.ls#2557