Handle canvas framebuffer scaling.

[luigifcruz]

This PR addresses an issue where glfwGetWindowSize and glfwGetFramebufferSize were incorrectly reporting the same values, despite the fact that the canvas native and normal dimensions were different. The proposed map is as follows:

glfwGetFramebufferSize() -> Module.canvas.[width, height]
glfwGetWindowSize() -> Module.canvas.[widthNative, heightNative]

This also scales the values returned from getCursorPos.

I thought about automatically resizing the canvas frame buffer size (canvas.[width, height]) according to the glfwGetMonitorContentScale but I imagine this would break a lot of software. The way I implemented this PR only makes a difference when the canvas frame buffer size is manually altered.

Fixes #19842 (?)

[luigifcruz]

Actually, this will break the cursor position if the glfwGetMonitorContentScale is above one and the glfwGetFramebufferSize and glfwGetFramebufferSize are the same. Automatically resizing the canvas frame buffer size might be necessary. Or ignoring _emscripten_get_device_pixel_ratio() and using the ratio between native and normal dimensions as the scaling factor.

Input from the community here would be appreciated as both options have pros and cons.

[luigifcruz]

Closed by #20584