[FIR] Add tests for top-level property initialization in scripts

- The test data is missing initialization checks and will be fixed with
  the subsequent commit.
- The test data is originally taken from
  `backingField/TopLevelPropertyInitialization` and has been simplified.
- I didn't add `const val` properties to the test data (compared to the
  original) due to KT-20110.

^KT-63286

compiler/testData/diagnostics/tests/script/topLevelPropertyInitialization.fir.kts

@@ -0,0 +1,58 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER -UNUSED_VARIABLE -ASSIGNED_BUT_NEVER_ACCESSED_VARIABLE -WRONG_INVOCATION_KIND
+// WITH_STDLIB
+
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.InvocationKind
+import kotlin.contracts.contract
+import kotlin.properties.ReadOnlyProperty
+
+@OptIn(ExperimentalContracts::class)
+inline fun <T> inPlaceRun(block: () -> T): T {
+    contract { callsInPlace(block, InvocationKind.EXACTLY_ONCE) }
+    return block()
+}
+
+fun <T> notInPlaceRun(block: () -> T): T = null!!
+
+fun <T> simpleDelegate(value: T): ReadOnlyProperty<Any?, T> = null!!
+
+@OptIn(ExperimentalContracts::class)
+fun <T> inPlaceDelegate(block: () -> T): ReadOnlyProperty<Any?, T> {
+    contract { callsInPlace(block, InvocationKind.EXACTLY_ONCE) }
+    return null!!
+}
+
+fun <T> notInPlaceDelegate(block: () -> T): ReadOnlyProperty<Any?, T> = null!!
+
+val a: String = a
+val b: String = inPlaceRun { b }
+val c: String = notInPlaceRun { c }
+
+val d: String by simpleDelegate(d)
+val e: String by inPlaceDelegate { e }
+val f: String by notInPlaceDelegate { f }
+
+val g: Int
+val h = 1.also { <!VAL_REASSIGNMENT!>g<!> = 2 }
+val i: Int
+val j by lazy { <!VAL_REASSIGNMENT!>i<!> = 2; 1 }
+val k: Int
+    get() {
+        <!VAL_REASSIGNMENT!>i<!> = 3
+        return i
+    }
+
+val l: Comparator<String> = object : Comparator<String> {
+    val delegate: Comparator<String> get() = n
+    override fun compare(o1: String, o2: String): Int = delegate.compare(o1, o2)
+}
+val m: Comparator<String> = object : Comparator<String> by n {}
+val n: Comparator<String> = Comparator { _, _ -> 0 }
+
+val t: String = z
+val u: String = inPlaceRun { z }
+val v: String = notInPlaceRun { z }
+val w: String by simpleDelegate(z)
+val x: String by inPlaceDelegate { z }
+val y: String by notInPlaceDelegate { z }
+val z: String = "VALUE"