Refine generic signature for fields

- For vals use the same semantics as for return types
- For vars use the same semantics as for value parameters

compiler/testData/writeSignature/declarationSiteVariance/wildcardOptimization/fields.kt

@@ -0,0 +1,25 @@
+class Out<out T>
+
+class Final
+open class Open
+
+@JvmField
+val NO_WILDCARDS: Out<Open> = Out()
+// field: FieldsKt::NO_WILDCARDS
+// generic signature: LOut<LOpen;>;
+
+@JvmField
+var HAS_WILDCARDS: Out<Open> = Out()
+// field: FieldsKt::HAS_WILDCARDS
+// generic signature: LOut<+LOpen;>;
+
+@JvmField
+var NO_WILDCARDS_VAR: Out<Final> = Out()
+// field: FieldsKt::NO_WILDCARDS_VAR
+// generic signature: LOut<LFinal;>;
+
+@JvmSuppressWildcards
+@JvmField
+var SUPPRESSED: Out<Open> = Out()
+// field: FieldsKt::SUPPRESSED
+// generic signature: LOut<LOpen;>;