refactor: generate KMP versions of equals and hashCode (#545)

Author: aajtodd

smithy-kotlin-codegen/src/main/kotlin/software/amazon/smithy/kotlin/codegen/rendering/StructureGenerator.kt

@@ -118,17 +118,17 @@ class StructureGenerator(
         writer.write("")
         writer.withBlock("override fun hashCode(): #Q {", "}", KotlinTypes.Int) {
             when {
-                sortedMembers.isEmpty() -> write("var result = javaClass.hashCode()")
+                sortedMembers.isEmpty() -> write("return this::class.hashCode()")
                 else -> {
                     write("var result = #1L#2L", memberNameSymbolIndex[sortedMembers[0]]!!.first, selectHashFunctionForShape(sortedMembers[0]))
                     if (sortedMembers.size > 1) {
                         sortedMembers.drop(1).forEach { memberShape ->
                             write("result = 31 * result + (#1L#2L)", memberNameSymbolIndex[memberShape]!!.first, selectHashFunctionForShape(memberShape))
                         }
                     }
+                    write("return result")
                 }
             }
-            write("return result")
         }
     }
 
@@ -170,7 +170,7 @@ class StructureGenerator(
         writer.write("")
         writer.withBlock("override fun equals(other: #Q?): #Q {", "}", KotlinTypes.Any, KotlinTypes.Boolean) {
             write("if (this === other) return true")
-            write("if (javaClass != other?.javaClass) return false")
+            write("if (other == null || this::class != other::class) return false")
             write("")
             write("other as #T", symbol)
             write("")

smithy-kotlin-codegen/src/test/kotlin/software/amazon/smithy/kotlin/codegen/rendering/StructureGeneratorTest.kt

@@ -134,7 +134,7 @@ class StructureGeneratorTest {
         val expected = """
             override fun equals(other: kotlin.Any?): kotlin.Boolean {
                 if (this === other) return true
-                if (javaClass != other?.javaClass) return false
+                if (other == null || this::class != other::class) return false
         
                 other as MyStruct
         
@@ -303,7 +303,7 @@ class StructureGeneratorTest {
         val expectedEqualsContent = """
             override fun equals(other: kotlin.Any?): kotlin.Boolean {
                 if (this === other) return true
-                if (javaClass != other?.javaClass) return false
+                if (other == null || this::class != other::class) return false
         
                 other as MyStruct