[Analysis API] add tests for delegate field

^KT-64584

analysis/low-level-api-fir/testData/getOrBuildFir/wholeDeclaration/delegate.kt

@@ -0,0 +1,12 @@
+<expr>
+class I(private val p: A) : A by p
+</expr>
+
+interface A {
+    var Int.zoo: Unit
+    fun foo()
+    fun Int.smth(): Short
+    val foo: Int
+    var bar: Long
+    val Int.doo: String
+}