Upgrade to Java 17 source and target compatibility

The next version of Ghidra should take advantage of the Java language features found in the latest LTS version: JDK 17.

The minimum supported version of Java should be upped to JDK 17.0.3, due to compiler bugs and security issues found in prior versions of JDK 17.

The current master branch c6cb8a0d85648c2f8d9a5a0f8cf2815c14e53520, which uses Java 11 source and target compatibility, is known to be compatible with JDK 17.0.3 for compilation and runtime with these settings, so users wishing to prepare their environments with JDK 17.0.3+ should be safe to do so.

NOTE: The minimum supported version of Gradle will need to be upped to Gradle 7.3.

Java code changes to support this are minimal and have already been implemented in 1996cdacd1d1bd7442c97cf694b6f27efb2b4fdb. The only remaining task (aside from documentation) should be to flip some version numbers in application.properties: https://github.com/NationalSecurityAgency/ghidra/blob/c6cb8a0d85648c2f8d9a5a0f8cf2815c14e53520/Ghidra/application.properties#L5-L8

[Wall-AF]

'Tworks!

[mumbel]

Nice! (20.04, openjdk 17.0.3, gradle 7.4.2)

I did run into eclipse hating life and trying to use an old gradle. Removed these two files (was just searching the gradle version string)

.gradle/buildOutputCleanup/cache.properties
gradle/wrapper/gradle-wrapper.properties