feat: add FileProvider class from AndroidX

This is for getting high quality camera images, and was a requirement for the code I need.

mastodon/src/main/AndroidManifest.xml

@@ -93,6 +93,16 @@
 			</intent-filter>
 		</receiver>
 
+		<provider
+			android:name="org.joinmastodon.android.utils.FileProvider"
+			android:authorities="${applicationId}.fileprovider"
+			android:exported="false"
+			android:grantUriPermissions="true">
+			<meta-data
+				android:name="android.support.FILE_PROVIDER_PATHS"
+				android:resource="@xml/file_paths" />
+		</provider>
+
 	</application>
 
 </manifest>