Fix parsing of unnamed patterns

[mrjameshamilton]

Before this PR

I came across FormatException of the form error: expected token: '_'; generated ) instead when using unnamed patterns, like the following (from the JEP):

class UnnamedPattern {
    public static void main(String[] args) {
        var cp = new ColoredPoint(new Point(1, 2), Color.RED);

        // The colour doesn't matter, so use an unnamed pattern
        // (as opposed to the unnamed type pattern `var _`).
        if (cp instanceof ColoredPoint(Point(int x, int y), _)) {
            System.out.println(x + "," + y);
        }

        if (cp instanceof ColoredPoint(_, var c)) {
            System.out.println(c);
        }
    }
}

record Point(int x, int y) { }
enum Color { RED, GREEN, BLUE }
record ColoredPoint(Point p, Color c) { }

I resolved this by overriding visitAnyPattern(AnyPatternTree node, Void unused) in the existing Java21InputAstVisitor.

However, AnyPatternTree is annotated as a preview feature in Java 21 so I changed Java versions from 21 to 23.

Before changing the version, I tried adding --enable-preview but then I got an error message that --enable-preview is not compatible with Java 11 source.

I also noticed Java 23 mentioned in the root build.gradle so I changed it to 23 rather than 22, 24, 25.

One thing I found in this change was that getImports() now returns a JCImportBase, so to ensure backwards compatibility I added an instanceof check that (and module imports support would need to be implemented in the future).

After this PR

==COMMIT_MSG==
Fix parsing of unnamed patterns
==COMMIT_MSG==

Possible downsides?

I'm not sure if changing Java versions from 21 to 23 (runtime in root build.gradle, target in palantir-java-format-spi/build.gradle and target in palantir-java-format/build.gradle) will have any negative effect? And if another solution should be found to resolve the issue.

[palantirtech]

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Description

Fix parsing of unnamed patterns

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