Add FIR enhancement tests, fix some exceptions / problems around them

Test data and tests themselves are based on
compiler/testData/loadJava/compiledJava

compiler/testData/loadJava/compiledJava/enum/EnumMembers.fir.txt

@@ -0,0 +1,4 @@
+public final enum class EnumMembers : R|java/lang/Enum<test/EnumMembers>| {
+    public open operator function first(): R|kotlin/Boolean|
+
+}

compiler/testData/loadJava/compiledJava/enum/EnumWithSpecializedEntry.fir.txt

@@ -0,0 +1,2 @@
+public open enum class EnumWithSpecializedEntry : R|java/lang/Enum<test/EnumWithSpecializedEntry>| {
+}

compiler/testData/loadJava/compiledJava/enum/JavaEnum.fir.txt

@@ -0,0 +1,2 @@
+public final enum class JavaEnum : R|java/lang/Enum<test/JavaEnum>| {
+}