Updatable Fonts in `ImGuiSystem`

[Doprez]

AFAIK there is currently no central way to change the font of the ImGui text. https://github.com/Eideren/StrideCommunity.ImGuiDebug/blob/effa2943ac583573cba5ceebce630151090db817/ImGuiSystem.cs#L214

I want to look into adding a public method that can take a Stride font and adding it to the ImGui interface during runtime and on initialization. If no font is found then it should fallback to what is currently the default ImGui IO font.

// Init
ImGuiIO& io = ImGui::GetIO();
ImFont* font1 = io.Fonts->AddFontFromFileTTF("font.ttf", size_pixels);
ImFont* font2 = io.Fonts->AddFontFromFileTTF("anotherfont.otf", size_pixels);