RFR: 8268320: Better error recovery for broken patterns in switch

[Jan Lahoda]

Trying to improve error recovery in case the user wanted to use a type-pattern in the switch construct, but didn't put a binding variable name after the type name. E.g.:

$ cat test/langtools/tools/javac/diags/examples/PatternExpected.java
[snip]
class PatternSwitch {
    private void doSwitch(Object o) {
        switch (o) {
            case String: break;
            default: break;
        }
    }
}
$ javac --enable-preview -source 17  test/langtools/tools/javac/diags/examples/PatternExpected.java
test/langtools/tools/javac/diags/examples/PatternExpected.java:32: error: type pattern expected
            case String: break;
                 ^
Note: test/langtools/tools/javac/diags/examples/PatternExpected.java uses preview features of Java SE 17.
Note: Recompile with -Xlint:preview for details.
1 error

-------------

Commit messages:
 - 8268320: Better error recovery for broken patterns in switch

Changes: https://git.openjdk.java.net/jdk/pull/4441/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4441&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8268320
  Stats: 160 lines in 7 files changed: 110 ins; 3 del; 47 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4441.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4441/head:pull/4441

PR: https://git.openjdk.java.net/jdk/pull/4441