Add hex-encoded version number to Engine singleton for easy comparisons

[akien-mga]

This makes it easier to do engine versions comparison from code, e.g.:

# The API used below is only available starting with Godot 3.1
var version = Engine.get_version_info()
if version.major > 3 || (version.major == 3 && version.minor >= 1):
    # GLES2 renders a black screen if WorldEnvironment background mode is "Canvas"
    if OS.get_current_video_driver() == OS.VIDEO_DRIVER_GLES2:
        $WorldEnvironment.environment.background_mode = Environment.BG_CLEAR_COLOR

becomes:

if Engine.get_version_info().hex >= 0x030100:
    # GLES2 renders a black screen if WorldEnvironment background mode is "Canvas"
    if OS.get_current_video_driver() == OS.VIDEO_DRIVER_GLES2:
        $WorldEnvironment.environment.background_mode = Environment.BG_CLEAR_COLOR

The above example is not really useful right now since this hex key is not available in 3.0, but we need to introduce it at some point to be usable for comparison between future releases :)

From experience in Godot's codebase (e.g. checking GCC versions), the non-hex variant above is very error prone and hard to read, so the hex-based version number is quite convenient and something I've seen in various libraries (e.g. OGRE).

[aaronfranke]

Ideally, this information should be included in projects as well. See also: #25497 and #25899

[akien-mga]

Ideally, this information should be included in projects as well. See also: #25497 and #25899

That's the plan eventually (though it will be the version string, not the hex one).

[akien-mga]

Now that Godot 3.1 has been released, we don't plan to cherry-pick new features and enhancements to the 3.0 branch, unless there is very strong support in favor of it. Removing cherrypick label for 3.0.