Fixed DPI Scaling issue

[xZekro51]

Fixes the DPI Scaling issue in the editor, especially when resizing the editor window.

• To load the System DPI scale, it relies on the currently unexposed method "glfwGetWindowContentScale" from GLFW (which is loaded by Silk) and should work across platforms.
• A variable called "UserScale" is added in the EditorTheme as an additional multiplier for the user to tune the Scaling as they like.