Convert util package to Kotlin (#1461)

* Rename .java to .kt

* Convert NonNullJsonAdapter

* Rename .java to .kt

* Convert NullSafeJsonAdapter

* Fix missing null-check

* Rename .java to .kt

* Convert Util (initial pass)

* Push to top-level Util

* Use extensions and properties where possible

* Use knownNotNull

* Spotless

* Clean up impl type classes a bit

* Update code gen

* Use extension for resolving

* Spotless

* Fix master conflicts

* Rename to toStringWithAnnotations()

* for (t in args.indices) {

* for (i in interfaces.indices) {

* Template

moshi-kotlin-tests/codegen-only/src/test/kotlin/com/squareup/moshi/kotlin/codegen/GeneratedAdaptersTest.kt

@@ -1270,7 +1270,7 @@ class GeneratedAdaptersTest {
   @Test fun customGenerator_withClassPresent() {
     val moshi = Moshi.Builder().build()
     val adapter = moshi.adapter<CustomGeneratedClass>()
-    val unwrapped = (adapter as NullSafeJsonAdapter<CustomGeneratedClass>).delegate()
+    val unwrapped = (adapter as NullSafeJsonAdapter<CustomGeneratedClass>).delegate
     assertThat(unwrapped).isInstanceOf(
       GeneratedAdaptersTest_CustomGeneratedClassJsonAdapter::class.java
     )