Introduce a build setting to detect Nightly builds. (#5852)

* Allow the AppIconBanner tool to be called with purely the build number.

And use that for the Element Pro Nightly.

* Use a build setting to determine Nightly builds.

ElementX/SupportingFiles/Info.plist

@@ -122,6 +122,8 @@
 	<string>$(CLASSIC_APP_KEYCHAIN_ACCESS_GROUP_IDENTIFIER)</string>
 	<key>classicAppKeychainServiceIdentifier</key>
 	<string>$(CLASSIC_APP_KEYCHAIN_SERVICE_IDENTIFIER)</string>
+	<key>isNightlyBuild</key>
+	<string>$(IS_NIGHTLY_BUILD)</string>
 	<key>keychainAccessGroupIdentifier</key>
 	<string>$(KEYCHAIN_ACCESS_GROUP_IDENTIFIER)</string>
 	<key>productionAppName</key>

ElementX/SupportingFiles/target.yml

@@ -77,6 +77,7 @@ targets:
         classicAppKeychainAccessGroupIdentifier: $(CLASSIC_APP_KEYCHAIN_ACCESS_GROUP_IDENTIFIER)
         classicAppDeepLinkURL: $(CLASSIC_APP_DEEP_LINK_URL)
         productionAppName: $(PRODUCTION_APP_NAME)
+        isNightlyBuild: $(IS_NIGHTLY_BUILD)
         ITSAppUsesNonExemptEncryption: false
         NSUserActivityTypes: [
           INSendMessageIntent,