OpenJDK 15 General Availability is scheduled for 2020/09/15

It contains a couple of language enhancements, that we should support:

• JEP 360: Sealed Classes (Preview)
  • http://cr.openjdk.java.net/~gbierman/jep360/jep360-20200526/specs/sealed-classes-jls.html
• JEP 375: Pattern Matching for instanceof (Second Preview)
• JEP 378: Text Blocks
• JEP 384: Records (Second Preview)
  • http://cr.openjdk.java.net/~gbierman/jep384/jep384-20200506/specs/records-jls.html

This issue is similar to the previous #2159

EA Release of JDK15 is available here: https://jdk.java.net/15/

Tasks:

• Add new java language versions 15 and 15-preview. Also add in KotlinTestingDsl.kt.
• Update asm dependency: https://search.maven.org/artifact/org.ow2.asm/asm
• Promote Text Blocks to a standard feature, there are no further changes from the last preview
• Update Records preview implementation, there are some changes (grammar, parser): "support additional forms of local classes and interfaces"
• Keep Pattern Matching preview implementation, there are no changes
• Add new Sealed Classes preview implementation (grammar, parser)
• Remove java language version 13-preview