[FIR Test] Migrate AbstractFirLoadCompiledKotlin to new test infrastructure

Also introduce two different modes for those tests:
- load metadata compiled with K1
- load metadata compiled with K2

compiler/testData/loadJava/compiledKotlin/visibility/PrivateClassMembers.fir.k2.txt

@@ -0,0 +1,16 @@
+public final class PrivateClassMembers : R|kotlin/Any| {
+    private final fun f(): R|kotlin/Int|
+
+    internal final val internal: R|kotlin/Int|
+        internal get(): R|kotlin/Int|
+
+    private final var r: R|kotlin/Int|
+        private get(): R|kotlin/Int|
+        private set(value: R|kotlin/Int|): R|kotlin/Unit|
+
+    private final val v: R|kotlin/Int|
+        private get(): R|kotlin/Int|
+
+    public constructor(): R|test/PrivateClassMembers|
+
+}

compiler/testData/loadJava/compiledKotlin/visibility/TopLevelVarWithPrivateSetter.fir.k1.txt

@@ -1,4 +1,3 @@
 internal final var topLevelVar: R|kotlin/Int|
     internal get(): R|kotlin/Int|
     private set(<set-?>: R|kotlin/Int|): R|kotlin/Unit|
-

compiler/testData/loadJava/compiledKotlin/visibility/TopLevelVarWithPrivateSetter.fir.k2.txt

@@ -0,0 +1,3 @@
+internal final var topLevelVar: R|kotlin/Int|
+    internal get(): R|kotlin/Int|
+    private set(value: R|kotlin/Int|): R|kotlin/Unit|