[core] Modularize FileSource codebase (#15768)

* [core] Introduce FileSourceManager and use it for default platform impl

  - Add `FileSourceManager` interface that provides access to `FileSource`
    instances and means of registering / unregistering `FileSource` factories
  - Split `DefaultFileSource` into smaller parts
  - Add `DatabaseFileSource` interface and it's default implementation
  - Remove inter-dependencies between concrete `FileSource` classes

* [build] Add files to next build system

* [core] Add generic property setters / getters

* [core] Remove setOnlineStatus from OnlineFileSource interface

* [core] Hide threading implementation details from DatabaseFileSource interface

* [core] Make DB file source methods virtual

* [core] Add documentation for DatabaseFileSource and rename one method

* [core] Use simple callback instead of ActorRef

* [core] Remove ActorRef from OnlineFileSource public header

* [core] Add callback to FileSource::forward async API

* [core] Pass OfflineRegionDefinition by value

* [core] Update tests to use modular file sources

* [core] Update unit tests

* [core] Update unit tests after rebase

* [core] Backport low prio fix for cached requests

* [core] Backport pack database

* [core] Return removed factory from unRegisterFileSourceFactory

* [core] Rename shadowed args in onlinefilesource

* [core] Remove simple std::function callback aliases

* [core] Expose online file source property keys in public header file

* [test-runner] Add proxy file source test runner

* [cache] Update mbgl-cache utility to use new file source

* [metrics] Rebaseline binary size metrics

* [offline] Update offline utility

* [core] Update changelog

2 files changed, 24 insertions, 22 deletions

diff --git a/src/mbgl/map/map.cpp b/src/mbgl/map/map.cpp
index a994af305f..061669f560 100644
--- a/src/mbgl/map/map.cpp
+++ b/src/mbgl/map/map.cpp
@@ -1,24 +1,24 @@
+#include <mbgl/annotation/annotation_manager.hpp>
+#include <mbgl/layermanager/layer_manager.hpp>
+#include <mbgl/map/camera.hpp>
 #include <mbgl/map/map.hpp>
 #include <mbgl/map/map_impl.hpp>
-#include <mbgl/map/camera.hpp>
 #include <mbgl/map/transform.hpp>
-#include <mbgl/annotation/annotation_manager.hpp>
-#include <mbgl/layermanager/layer_manager.hpp>
-#include <mbgl/style/style_impl.hpp>
-#include <mbgl/style/observer.hpp>
-#include <mbgl/renderer/update_parameters.hpp>
+#include <mbgl/math/log2.hpp>
 #include <mbgl/renderer/renderer_frontend.hpp>
 #include <mbgl/renderer/renderer_observer.hpp>
-#include <mbgl/storage/file_source.hpp>
+#include <mbgl/renderer/update_parameters.hpp>
+#include <mbgl/storage/file_source_manager.hpp>
 #include <mbgl/storage/resource.hpp>
 #include <mbgl/storage/response.hpp>
+#include <mbgl/style/observer.hpp>
+#include <mbgl/style/style_impl.hpp>
 #include <mbgl/util/constants.hpp>
-#include <mbgl/util/math.hpp>
 #include <mbgl/util/exception.hpp>
+#include <mbgl/util/logging.hpp>
 #include <mbgl/util/mapbox.hpp>
+#include <mbgl/util/math.hpp>
 #include <mbgl/util/tile_coordinate.hpp>
-#include <mbgl/util/logging.hpp>
-#include <mbgl/math/log2.hpp>
 
 #include <utility>
 
@@ -30,9 +30,11 @@ Map::Map(RendererFrontend& frontend,
          MapObserver& observer,
          const MapOptions& mapOptions,
          const ResourceOptions& resourceOptions)
-    : impl(std::make_unique<Impl>(frontend, observer,
-                                  FileSource::getSharedFileSource(resourceOptions),
-                                  mapOptions)) {}
+    : impl(std::make_unique<Impl>(
+          frontend,
+          observer,
+          FileSourceManager::get() ? FileSourceManager::get()->getFileSource(ResourceLoader, resourceOptions) : nullptr,
+          mapOptions)) {}
 
 Map::Map(std::unique_ptr<Impl> impl_) : impl(std::move(impl_)) {}
 
diff --git a/src/mbgl/map/map_impl.cpp b/src/mbgl/map/map_impl.cpp
index 69c3de9783..bc2a37fe07 100644
--- a/src/mbgl/map/map_impl.cpp
+++ b/src/mbgl/map/map_impl.cpp
@@ -11,15 +11,15 @@ Map::Impl::Impl(RendererFrontend& frontend_,
                 MapObserver& observer_,
                 std::shared_ptr<FileSource> fileSource_,
                 const MapOptions& mapOptions)
-        : observer(observer_),
-          rendererFrontend(frontend_),
-          transform(observer, mapOptions.constrainMode(), mapOptions.viewportMode()),
-          mode(mapOptions.mapMode()),
-          pixelRatio(mapOptions.pixelRatio()),
-          crossSourceCollisions(mapOptions.crossSourceCollisions()),
-          fileSource(std::move(fileSource_)),
-          style(std::make_unique<style::Style>(*fileSource, pixelRatio)),
-          annotationManager(*style) {
+    : observer(observer_),
+      rendererFrontend(frontend_),
+      transform(observer, mapOptions.constrainMode(), mapOptions.viewportMode()),
+      mode(mapOptions.mapMode()),
+      pixelRatio(mapOptions.pixelRatio()),
+      crossSourceCollisions(mapOptions.crossSourceCollisions()),
+      fileSource(std::move(fileSource_)),
+      style(std::make_unique<style::Style>(fileSource, pixelRatio)),
+      annotationManager(*style) {
     transform.setNorthOrientation(mapOptions.northOrientation());
     style->impl->setObserver(this);
     rendererFrontend.setObserver(*this);