FIR: Support coercion-to-unit semantics for callable references

compiler/fir/analysis-tests/testData/resolveWithStdlib/callableReferences/coercionToUnit.kt

@@ -0,0 +1,9 @@
+public fun <T> T.myAlso(block: (T) -> Unit): T = TODO()
+
+class B {
+    fun add(x: String): Boolean = true
+}
+
+fun main(b: B) {
+    "".myAlso(b::add)
+}