[Kotlin] fix wrong type- and importMapping for kotlinx.date (#17597) (#18488)

Author: ch4rl3x

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/KotlinClientCodegen.java

@@ -578,9 +578,14 @@ private void processJava8Date(String dateLibrary) {
     private void processKotlinxDate() {
         additionalProperties.put(DateLibrary.KOTLINX_DATETIME.value, true);
 
-        typeMapping.put("date-time", "kotlinx.datetime.Instant");
+        typeMapping.put("date-time", "Instant");
+        typeMapping.put("date", "LocalDate");
+
         typeMapping.put("DateTime", "Instant");
+        typeMapping.put("Date", "LocalDate");
+
         importMapping.put("Instant", "kotlinx.datetime.Instant");
+        importMapping.put("LocalDate", "kotlinx.datetime.LocalDate");
     }
 
     private void processJVMRetrofit2Library(String infrastructureFolder) {