[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

render-test/file_source.cpp

@@ -1,6 +1,11 @@
+#include <mbgl/storage/file_source_manager.hpp>
+#include <mbgl/storage/resource.hpp>
 #include <mbgl/storage/resource_options.hpp>
+#include <mbgl/util/async_request.hpp>
 #include <mbgl/util/logging.hpp>
 
+#include <atomic>
+
 #include "file_source.hpp"
 
 namespace mbgl {
@@ -10,8 +15,14 @@ std::atomic_size_t transferredSize{0};
 std::atomic_bool active{false};
 std::atomic_bool offline{true};
 
-ProxyFileSource::ProxyFileSource(const std::string& cachePath, const std::string& assetPath)
-    : DefaultFileSource(cachePath, assetPath, false) {}
+ProxyFileSource::ProxyFileSource(std::shared_ptr<FileSource> defaultResourceLoader_, const ResourceOptions& options)
+    : defaultResourceLoader(std::move(defaultResourceLoader_)) {
+    assert(defaultResourceLoader);
+    if (offline) {
+        auto dbfs = FileSourceManager::get()->getFileSource(FileSourceType::Database, options);
+        dbfs->setProperty("read-only-mode", true);
+    }
+}
 
 ProxyFileSource::~ProxyFileSource() = default;
 
@@ -43,7 +54,7 @@ std::unique_ptr<AsyncRequest> ProxyFileSource::request(const Resource& resource,
         }
     }
 
-    return DefaultFileSource::request(transformed, [=](Response response) {
+    return defaultResourceLoader->request(transformed, [=](Response response) {
         if (transformed.loadingMethod == Resource::LoadingMethod::CacheOnly && response.noContent) {
             if (transformed.kind == Resource::Kind::Tile && transformed.tileData) {
                 mbgl::Log::Info(mbgl::Event::Database,
@@ -64,19 +75,6 @@ std::unique_ptr<AsyncRequest> ProxyFileSource::request(const Resource& resource,
     });
 }
 
-std::shared_ptr<FileSource> FileSource::createPlatformFileSource(const ResourceOptions& options) {
-    auto fileSource = std::make_shared<ProxyFileSource>(options.cachePath(), options.assetPath());
-
-    fileSource->setAccessToken(options.accessToken());
-    fileSource->setAPIBaseURL(options.baseURL());
-
-    if (offline) {
-        fileSource->reopenDatabaseReadOnlyForTesting();
-    }
-
-    return fileSource;
-}
-
 // static
 void ProxyFileSource::setOffline(bool status) {
     offline = status;