* Backend: remove RenderTargetFlag and refactor depth/stencil state setup
* Fix Z-test and Z-write being enabled by default for main queue
* GL: fix framebuffer attachment not being cleared
* Use dirtyFlags for RenderTarget update
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Co-authored-by: halx99 <halx99@live.com>
* Fix memory leaks when axmol apps exit on non-embed systems
1. DriverBase no destroyInstance
2. Every object inherited from ax::Ref shoud destory before ScriptEngineManager, otherwise will trigger it's reinit and leak
3. QuadCommand always leak isolated indices
4. static singleton should'nt inhert from ax::Ref due to destory it before ScriptEngineManager impossible
5. Make Director don't inherit from ax::Ref due to it also cause ScriptEngineManager re-init, because we destroy ScriptEngineManger in destructor of Director
6. Explicit Director managed by Application and don't delete self at purgeDirector, since it will release at mainLoop and re-init in glView->pollEvents then leak
7. Rename ApplicationProtocol to ApplicationBase
8. Rename purgeDirector since we don't delete director self at it, maye rename to cleanup
9. Change ShaderCache to new/delete singleton, managed by ProgramManager
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Co-authored-by: lich426 <lich426@gmail.com>
smilediver