[fenix] change name for isFirstRun to isFirstNimbusRun and move setter to after experiments are set

app/src/main/java/org/mozilla/fenix/experiments/NimbusSetup.kt

@@ -80,7 +80,7 @@ fun createNimbus(context: Context, url: String?): NimbusApi {
             // and would mostly produce the value `Beta` and rarely would produce `beta`.
             channel = BuildConfig.BUILD_TYPE,
             customTargetingAttributes = mapOf(
-                "isFirstRun" to context.settings().isFirstRun.toString()
+                "isFirstRun" to context.settings().isFirstNimbusRun.toString()
             )
         )
         Nimbus(context, appInfo, serverSettings, errorReporter).apply {
@@ -101,9 +101,9 @@ fun createNimbus(context: Context, url: String?): NimbusApi {
                 globalUserParticipation = enabled
             }
 
-            if (context.settings().isFirstRun || url.isNullOrBlank()) {
-                context.settings().isFirstRun = false
+            if (context.settings().isFirstNimbusRun || url.isNullOrBlank()) {
                 setExperimentsLocally(R.raw.initial_experiments)
+                context.settings().isFirstNimbusRun = false
             }
 
             // We may have downloaded experiments on a previous run, so let's start using them

app/src/main/java/org/mozilla/fenix/utils/Settings.kt

@@ -347,7 +347,7 @@ class Settings(private val appContext: Context) : PreferencesHolder {
         default = false
     )
 
-    val isFirstRun: Boolean by booleanPreference(
+    var isFirstNimbusRun: Boolean by booleanPreference(
         appContext.getPreferenceKey(R.string.pref_key_is_first_run),
         default = true
     )