set java toolchain version in all projects related to Java

mppAndroidProject.gradle

@@ -24,3 +24,9 @@ kotlin {
 }
 
 apply from: "$defaultAndroidSettingsPresetPath"
+
+java {
+    toolchain {
+        languageVersion = JavaLanguageVersion.of(8)
+    }
+}

mppJavaProject.gradle

@@ -26,3 +26,9 @@ kotlin {
         }
     }
 }
+
+java {
+    toolchain {
+        languageVersion = JavaLanguageVersion.of(8)
+    }
+}

mppProjectWithSerialization.gradle

@@ -48,3 +48,9 @@ kotlin {
 }
 
 apply from: "$defaultAndroidSettingsPresetPath"
+
+java {
+    toolchain {
+        languageVersion = JavaLanguageVersion.of(8)
+    }
+}