[FIR] Add test data

compiler/testData/diagnostics/tests/properties/backingField/trivialExplicitBackingFIeld.fir.kt

@@ -0,0 +1,4 @@
+class A {
+    val number: Number
+        field = 1
+}

compiler/testData/diagnostics/tests/properties/backingField/trivialExplicitBackingFIeld.kt

@@ -0,0 +1,4 @@
+class A {
+    <!MUST_BE_INITIALIZED_OR_BE_ABSTRACT!>val number: Number<!>
+        <!EXPLICIT_BACKING_FIELDS_UNSUPPORTED!>field = 1<!>
+}

compiler/testData/diagnostics/tests/properties/backingField/trivialExplicitBackingFIeld.txt

@@ -0,0 +1,9 @@
+package
+
+public final class A {
+    public constructor A()
+    public final val number: kotlin.Number
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}