Apply Java migration: pattern variables

[Baltoli]

This is a fully-mechanical PR that uses IntelliJ to migrate to using the new Java feature for pattern variables in instanceof checks. For example, this code:

            if (left instanceof KApply) {
                KApply kapp = (KApply) left;
                Production prod = production(kapp);

becomes:

            if (left instanceof KApply kapp) {
                Production prod = production(kapp);

which saves a lot of boilerplate code.

There are no manual changes or decisions in this PR; it's push-button only.