RFR: JDK-8240998: Implement javac changes for deconstruction patterns.

[Jan Lahoda]

Hi,

I would like to ask for a review for a patch that implements the 
deconstruction patterns, as described in JEP 375:
https://bugs.openjdk.java.net/browse/JDK-8235186

The current specification draft is here:
http://cr.openjdk.java.net/~gbierman/jep375/jep375-20200316/specs/patterns-instanceof-jls.html

For this phase, the proposal is for javac to desugar the deconstruction 
patterns using record accessors.

The CSR for this change is being written here:
https://bugs.openjdk.java.net/browse/JDK-8240999

The proposed patch:
http://cr.openjdk.java.net/~jlahoda/8240998/webrev.00

JBS: https://bugs.openjdk.java.net/browse/JDK-8240998

Any feedback is welcome!

Thanks,
     Jan