Fix fileprovider build with androidx

When androidx is enabled, the android support library is no longer
available. The library artifact needs to be replaced as well as changing
code to use the `FileProvider` class from `androidx.core.content`
instead of `android.support.v4.content`.

Author: dbnicholson

pythonforandroid/bootstraps/common/build/templates/build.tmpl.gradle

@@ -130,6 +130,12 @@ dependencies {
     {% if args.presplash_lottie %}
     implementation 'com.airbnb.android:lottie:3.4.0'
     {%- endif %}
+    {% if args.fileprovider_paths %}
+    {%- if args.enable_androidx -%}
+    implementation 'androidx.core:core:1.8.0'
+    {%- else -%}
     implementation 'com.android.support:support-v4:26.1.0'
+    {%- endif -%}
+    {% endif %}
 }