Fix canvas resize options when using EmscriptenFullscreenStrategy

[devappd]

See JSEvents_resizeCanvasForFullscreen, where strategy is supplied.

Our resize options resizeCanvasOnFullscreenChange and adjustViewportByDevicePixelRatio are appropriate when using the default strategy (via emscripten_request_fullscreen()). However, this differs when specifying the strategy by emscripten_request_fullscreen_strategy() and emscripten_request_softfullscreen():

• EMSCRIPTEN_FULLSCREEN_CANVAS_SCALE_NONE does not apply any canvas sizing behavior. This is default.
• EMSCRIPTEN_FULLSCREEN_CANVAS_SCALE_STDDEF is equivalent to { resizeCanvasOnFullscreenChange: true, adjustViewportByDevicePixelRatio: false}
• EMSCRIPTEN_FULLSCREEN_CANVAS_SCALE_HIDEF is equivalent to { resizeCanvasOnFullscreenChange: true, adjustViewportByDevicePixelRatio: true}

Resolution

• Make resizeCanvasOnFullscreenChange and adjustViewportByDevicePixelRatio into private variables
• When triggering fullscreen from JS-side, set these both true
• Patch JSEvents.resizeCanvasForFullscreen to set these both variables to true if EMSCRIPTEN_FULLSCREEN_CANVAS_SCALE_NONE, otherwise set both variables to false
• Disable all the above behavior if resizeCanvasOnElementSizing is false
• fixCanvasViewport is still necessary for non-fullscreen operations. In the canvas resize handler, attach this call to resizeCanvasOnElementSizing instead of adjustViewportByDevicePixelRatio.
• Expose EMSCRIPTEN_FULLSCREEN_FILTERING_NEAREST/BILINEAR (CSS is only changed from default for NEAREST -- image-rendering: optimize-speed;

Notes

• How well does soft-fullscreen work in React, etc.?
• If I want to implement scaled canvas sizing (render at half resolution, etc.), I have to do so on JS-side; emscripten does not provide functions for this