Optimize isReferenceTo() when searching for PsiMethod usages

Avoid resolving references when we know from context that a reference
at given location can't resolve to a PsiMethod.

idea/testData/findUsages/java/findJavaMethodUsages/UnaryNot.0.java

@@ -0,0 +1,7 @@
+// PSI_ELEMENT: com.intellij.psi.PsiMethod
+// OPTIONS: usages
+public class UnaryNot {
+    public UnaryNot <caret>not() {
+        return this;
+    }
+}