Draft: Resolve "Upgrade to Java 21"

Closes #1805

The following recipes were applied:

• org.openrewrite.java.migrate.UpgradeToJava17
• org.openrewrite.java.migrate.UpgradeBuildToJava21
• org.openrewrite.staticanalysis.RemoveExtraSemicolons
• org.openrewrite.java.migrate.util.SequencedCollection
• org.openrewrite.java.migrate.lang.SwitchCaseAssignmentsToSwitchExpression
• org.openrewrite.java.migrate.lang.SwitchCaseReturnsToSwitchExpression
• org.openrewrite.java.migrate.UpgradeToJava21 (re-applied to check recipes consistency when applied one by one)

Work left:

• Homogenize code format
• Try to replace with var
• Replace commit author with "OpenRewrite"
• Try to replace with records whenever possible (put deprecated on getter methods in such case)
• Change commit messages to specify recipe used every time
• Edit cicd image to use appropriate JDK
• Re-run UpgradeToJava21 one last time right before merge to account for issues merged in between