Part 1 - Refactor Featurelist

The "feature.h" as is is a bit heavy: 
-> We do have a new Allocation of Feature for every feature
-> We do track the pointers in both a hashmap and qlist
-> Each feature QString is created from a UTF-8 char, so each QString needs an allocation too!

Add to that that the evaluation algorightm of feature -> bool (is this on?) - needs to check multiple std::functions 
a String Based List lookup for possible dependencies. A roundtrip to a settingslist to check if we ever feature-flip from guardian.

No optimization is possible, even if we mark a Feature with "FeatureCallback_false" - given we construct the list at runtime, 
fetch a Feature* via a QString and then check a std::func* - these are too many layers for the compiler to determine "this is always false".

The reality is, the majority of our feature-flags are Fixed and Non Changeable by the time the Compiler has evaluated the defines. 
So we are paying a lot to have flexibility we actually never use and we are paying that on every start of the app. 

My proposal is to swap this into a "Pay What you need" model with 3 Tiers of FeatureFlags: 

-> Static Feature: They are determined at compiletime. i.e "is this windows?" They need no allocation, just live in the data section. 
They are constexpr the compiler can do code-elimination on dead codepaths. 

-> Runtime Feature: A wrapper around func -> Bool; They are run on every check, i.e "deactivate windows-split-tunnel when mullvad is detected". 

-> Dynamic Feature: A simplified version of our current Feature*, it has a func->bool for the base value. Overrides via the dev-menu are possibile. 
Also they support overrides from guardian. 



As none of these features are QObjects, for FeatureModel i add a "ViewModel" Class FeatureProxy(feature::any) that can take a ref for any feature and expose 
a Feature to QML. The API for QML is unchanged, only in c++ land we have to change callers.

Author: strseb

src/cmake/shared-sources.cmake

@@ -22,8 +22,6 @@ target_sources(shared-sources INTERFACE
     ${CMAKE_SOURCE_DIR}/src/constants.h
     ${CMAKE_SOURCE_DIR}/src/constants.cpp
     ${CMAKE_SOURCE_DIR}/src/settingslist.h
-    ${CMAKE_SOURCE_DIR}/src/feature/featurelist.h
-    ${CMAKE_SOURCE_DIR}/src/feature/experimentalfeaturelist.h
     ${CMAKE_SOURCE_DIR}/src/addons/addon.cpp
     ${CMAKE_SOURCE_DIR}/src/addons/addon.h
     ${CMAKE_SOURCE_DIR}/src/addons/addonapi.cpp
@@ -78,8 +76,12 @@ target_sources(shared-sources INTERFACE
     ${CMAKE_SOURCE_DIR}/src/env.h
     ${CMAKE_SOURCE_DIR}/src/errorhandler.cpp
     ${CMAKE_SOURCE_DIR}/src/errorhandler.h
-    ${CMAKE_SOURCE_DIR}/src/feature/feature.cpp
-    ${CMAKE_SOURCE_DIR}/src/feature/feature.h
+    ${CMAKE_SOURCE_DIR}/src/feature/features.h
+    ${CMAKE_SOURCE_DIR}/src/feature/features.cpp
+    ${CMAKE_SOURCE_DIR}/src/feature/featuretypes.h
+    ${CMAKE_SOURCE_DIR}/src/feature/featuretypes.cpp
+    ${CMAKE_SOURCE_DIR}/src/feature/featureproxy.cpp
+    ${CMAKE_SOURCE_DIR}/src/feature/featureproxy.h
     ${CMAKE_SOURCE_DIR}/src/feature/taskgetfeaturelist.cpp
     ${CMAKE_SOURCE_DIR}/src/feature/taskgetfeaturelist.h
     ${CMAKE_SOURCE_DIR}/src/feature/taskgetfeaturelistworker.cpp

src/cmake/sources.cmake

@@ -20,9 +20,6 @@ set_property(TARGET mozillavpn-sources PROPERTY INTERFACE_INCLUDE_DIRECTORIES
 # VPN Client source files
 target_sources(mozillavpn-sources INTERFACE
     ${CMAKE_CURRENT_SOURCE_DIR}/accessiblenotification.cpp
-    ${CMAKE_CURRENT_SOURCE_DIR}/feature/featurelistcallback.h
-    ${CMAKE_CURRENT_SOURCE_DIR}/feature/featurelist.h
-    ${CMAKE_CURRENT_SOURCE_DIR}/feature/experimentalfeaturelist.h
     ${CMAKE_CURRENT_SOURCE_DIR}/appimageprovider.h
     ${CMAKE_CURRENT_SOURCE_DIR}/applistprovider.h
     ${CMAKE_CURRENT_SOURCE_DIR}/apppermission.cpp