fix: preserve guarded multi-pattern hierarchy

[martinfrancois]

Summary

Preserve both patterns and the separate boolean guard in a switch label such as case First _, Second _ when enabled.

Fixes #6808.

Problem

First _ and Second _ are two alternative patterns: the first matches a First value and the second matches a Second value. enabled is a separate boolean guard. Spoon must build one CtCasePattern for each alternative and attach enabled as the CtCase guard.

ECJ stores the two patterns inside one EitherOrMultiPattern, then wraps that node and the guard condition in a GuardedPattern. For this label, the correct alternative count is two. Spoon uses that count while it receives ECJ's child nodes: the first two pattern children belong to the comma-separated label, and the following expression is the guard.

Spoon counted alternatives only when EitherOrMultiPattern was the direct case expression. The wrapper therefore made Spoon expect one pattern instead of two. Spoon attached First _ correctly, then treated the CtTypePattern for Second _ as the guard. Model construction failed because a CtTypePattern belongs under a CtCasePattern, not directly under a CtCase guard.

Change

• Unwrap the ECJ GuardedPattern only while counting its alternatives.
• Create one CtCasePattern for each alternative.
• Keep each CtTypePattern below its CtCasePattern.
• Attach the real guard to the CtCase.

Tests

• Added a regression that checks both alternatives, their node types, all parent links, and the guard parent.
• mvn -q -Dtest=spoon.test.pattern.SwitchPatternTest#testMultipleTypePatternsWithGuardInSwitch test passes.
• The complete switch and record-pattern suites pass: 17 tests.
• mvn -q -DskipTests install and mvn -q spotless:check pass.
• StoneDetector processes OpenJDK Unnamed.java: AST 1/1, CFG 4/4, dominators 4/4, paths 4/4, and no reported errors.
• Direct model inspection confirms that both guarded alternatives are retained.

Full test suite

The complete Java 25 suite passes 4,461 tests with 0 failures, 0 errors, and 16 skipped.