RFR: 8341901: Using 'var' keyword switch pattern matching causes compiler error

[Jan Lahoda]

Consider code like:

public class T {
   record R(N.I i) {}
   int test(Object o) {
       return switch (o) {
           case R(var nested) -> 0;
           default -> 0;
       };
   }
   static class N<T> {
       interface I {}
   }
}


This fails to compile since JDK 23, due to:

$ javac T.java 
error: cannot select a static class from a parameterized type
1 error


The reason for the error is this: the type of `nested` is inferred to `T.N.I`. This is correct. javac will then construct a synthetic AST for it, and the AST will be structurally correct as well: `T.N.I`. But a) the `Type` attached to `T.N` will be `T.N<T>` (which by itself is not correct), and b) after the synthetic AST is created, `Check.validate` is called on the type's AST, and fails, as the types is sees correspond to `T.N<T>.I`, which is illegal.

Note the synthetic AST is also set for local variable type inference, but the `validate` is called *before* the synthetic AST is created.

This PR proposes to do two things:
- move the `validate` call before the synthetic AST creation for `visitBindingPattern`, to mimic the behavior for `var`s.
- the `TreeMaker` is tweaked to inject erased types instead of parameterized types when generating qualified identifiers for classes or interfaces. This should correspond more closely to what happens when one types `T.N.I` in the source code.

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

Commit messages:
 - Removing trailing whitespace.
 - Only erase in QualIdent
 - Only erase types for classes
 - 8341901: Using 'var' keyword switch pattern matching causes compiler error

Changes: https://git.openjdk.org/jdk/pull/21495/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21495&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8341901
  Stats: 102 lines in 3 files changed: 99 ins; 1 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/21495.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21495/head:pull/21495

PR: https://git.openjdk.org/jdk/pull/21495