CommonsApplication migrate to kotlin & some lint fixes (#5879)

* convert to kotlin

Signed-off-by: parneet-guraya <gurayaparneet@gmail.com>

* use lateinit instead of nullable types

Signed-off-by: parneet-guraya <gurayaparneet@gmail.com>

* instance property access fix

Signed-off-by: parneet-guraya <gurayaparneet@gmail.com>

* refactor constants name with uppercased ones

Signed-off-by: parneet-guraya <gurayaparneet@gmail.com>

* remove unused

Signed-off-by: parneet-guraya <gurayaparneet@gmail.com>

* fix imports in test

Signed-off-by: parneet-guraya <gurayaparneet@gmail.com>

* use mockk for kotlin to fix tests

Signed-off-by: parneet-guraya <gurayaparneet@gmail.com>

---------

Signed-off-by: parneet-guraya <gurayaparneet@gmail.com>

Author: parneet-guraya

app/src/androidTest/java/fr/free/nrw/commons/AboutActivityTest.kt

@@ -105,7 +105,7 @@ class AboutActivityTest {
     fun testLaunchTranslate() {
         Espresso.onView(ViewMatchers.withId(R.id.about_translate)).perform(ViewActions.click())
         Espresso.onView(ViewMatchers.withId(android.R.id.button1)).perform(ViewActions.click())
-        val langCode = CommonsApplication.getInstance().languageLookUpTable.codes[0]
+        val langCode = CommonsApplication.instance.languageLookUpTable!!.codes[0]
         Intents.intended(
             CoreMatchers.allOf(
                 IntentMatchers.hasAction(Intent.ACTION_VIEW),