[Reader] Embed a PDF decoder as the fallback in case of failure of the WinRT one

[LancerComet]

Some users use a shrunk version of Windows that doesn't have the WinRT PDF component. Give it a fallback when it is unavailable.

• [x] Add an embedded PDF codec as the fallback.
• [x] Make a switch for it. Let user decide.

[LancerComet]

Done