Add @Json.ignore (#1417)

* Default Json.name to an unset value

* Promote shared transient tests to DualKotlinTest

* Add new ignore property to Json

* Support it in ClassJsonAdapter

* Mention no enum/record support

* Support in KotlinJsonAdapter

* Rework code gen API to know of "ignored"

* Support in apt code gen

* Support in KSP

* Update old non-working transient example test

* Synthetic holders

* Use field on both

kotlin/tests/extra-moshi-test-module/build.gradle.kts

@@ -17,3 +17,7 @@
 plugins {
   kotlin("jvm")
 }
+
+dependencies {
+  implementation(project(":moshi"))
+}