Take release level into account when check for java9

Currently in SearchableEnvironment we only check if the project level is
larger java9plus but when constructing a release specific
SearchableEnvironment this needs to take the release option into account
instead.

Fix #4399

Author: laeubi

org.eclipse.jdt.core.tests.model/src/org/eclipse/jdt/core/tests/model/ReconcilerMultiReleaseTests.java

@@ -2,6 +2,7 @@
 
 import junit.framework.Test;
 import org.eclipse.core.runtime.CoreException;
+import org.eclipse.core.runtime.IPath;
 import org.eclipse.core.runtime.NullProgressMonitor;
 import org.eclipse.jdt.core.IClasspathAttribute;
 import org.eclipse.jdt.core.IClasspathEntry;
@@ -45,9 +46,16 @@ public IProblemRequestor getProblemRequestor(ICompilationUnit unit) {
 	@Override
 	public void setUpSuite() throws Exception {
 		super.setUpSuite();
-
+		//Because we use 1.8 compliance on the project, tje JCL21 wil not be setup automatically so we need to to it explicitly.
+		if (JavaCore.getClasspathVariable("JCL_21_LIB") == null) {
+			setupExternalJCL("jclMin21");
+			JavaCore.setClasspathVariables(
+				new String[] {"JCL_21_LIB", "JCL_21_SRC", "JCL_SRCROOT"},
+				new IPath[] {getExternalJCLPath("21"), getExternalJCLSourcePath("21"), getExternalJCLRootSourcePath()},
+				null);
+		}
 		IJavaProject mrproject = createJavaProject("ReconcilerMR", new String[] { "src", "src9", "src21" },
-				new String[] { "JCL18_LIB" }, "bin");
+				new String[] { "JCL_21_LIB" }, "bin");
 		createFolder("/ReconcilerMR/src/p");
 		createFolder("/ReconcilerMR/src9/p");
 		createFolder("/ReconcilerMR/src21/p");
@@ -136,6 +144,8 @@ public class D {
 					void m(B b) {
 						// Calling method m only available from Java 21+
 						b.m();
+						// Calling a JDK class should work
+						System.out.println("Testme");
 					}
 				}
 			""";

org.eclipse.jdt.core/model/org/eclipse/jdt/internal/core/SearchableEnvironment.java

@@ -115,7 +115,7 @@ public SearchableEnvironment(JavaProject project, org.eclipse.jdt.core.ICompilat
 			|| !JavaCore.IGNORE.equals(project.getOption(JavaCore.COMPILER_PB_DISCOURAGED_REFERENCE, true));
 		this.workingCopies = workingCopies;
 		this.nameLookup = project.newNameLookup(workingCopies, excludeTestCode);
-		boolean java9plus = JavaCore.callReadOnly(() -> CompilerOptions
+		boolean java9plus = release >=JavaProject.FIRST_MULTI_RELEASE || JavaCore.callReadOnly(() -> CompilerOptions
 				.versionToJdkLevel(project.getOption(JavaCore.COMPILER_COMPLIANCE, true)) >= ClassFileConstants.JDK9);
 		if (java9plus) {
 			this.knownModuleLocations = new HashMap<>();