[kotlin][client] small improvements (#9640)

* [kotlin][client] standardize adapter type names

* [kotlin][client] remove unused class

* [kotlin][client] fix IDE warning

* [kotlin][client] improve import layout

* [kotlin][client] update sample projects

samples/client/petstore/kotlin-json-request-string/src/main/kotlin/org/openapitools/client/infrastructure/ApiClient.kt

@@ -1,7 +1,6 @@
 package org.openapitools.client.infrastructure
 
 import android.os.Build
-import okhttp3.Credentials
 import okhttp3.OkHttpClient
 import okhttp3.RequestBody
 import okhttp3.RequestBody.Companion.asRequestBody

samples/client/petstore/kotlin-json-request-string/src/main/kotlin/org/openapitools/client/infrastructure/Serializer.kt

@@ -12,7 +12,7 @@ object Serializer {
         .add(LocalDateAdapter())
         .add(UUIDAdapter())
         .add(ByteArrayAdapter())
-        .add(UriAdapter())
+        .add(URIAdapter())
         .add(KotlinJsonAdapterFactory())
         .add(BigDecimalAdapter())
         .add(BigIntegerAdapter())

samples/client/petstore/kotlin-json-request-string/src/main/kotlin/org/openapitools/client/infrastructure/URIAdapter.kt

@@ -4,10 +4,10 @@ import com.squareup.moshi.FromJson
 import com.squareup.moshi.ToJson
 import java.net.URI
 
-class UriAdapter {
+class URIAdapter {
     @ToJson
     fun toJson(uri: URI) = uri.toString()
 
     @FromJson
-    fun fromJson(s: String) = URI.create(s)
+    fun fromJson(s: String): URI = URI.create(s)
 }

samples/client/petstore/kotlin-json-request-string/src/main/kotlin/org/openapitools/client/infrastructure/UUIDAdapter.kt

@@ -9,5 +9,5 @@ class UUIDAdapter {
     fun toJson(uuid: UUID) = uuid.toString()
 
     @FromJson
-    fun fromJson(s: String) = UUID.fromString(s)
+    fun fromJson(s: String): UUID = UUID.fromString(s)
 }