Duplicate track action added

[PedroHugoNoevo]

This solves issue #15029

[akien-mga]

Done

Please amend your commit log to be more explicit, this doesn't tell us anything about what the commit implements. It should read something like:

Add duplicate track action to AnimationPlayer

Fixes #15029.

See https://github.com/godotengine/godot/blob/master/CONTRIBUTING.md#format-your-commit-logs-with-readability-in-mind and PR workflow.

[akien-mga]

There are also some style issues: https://travis-ci.org/godotengine/godot/jobs/464914837

You can use clang-format to make sure your code style matches our guidelines.

[akien-mga]

Moving to 3.2 milestone as we're about to enter the beta stage and release freeze for Godot 3.1. Only bug fixes against issues of the 3.1 milestone (or enhancements to core features of the 3.1 roadmap) will be considered until 3.1-stable is released.

Note: If it's merged after 3.1-stable is released, this change may be considered for cherry-picking into a later 3.1.x release.

[Calinou]

@PedroHugoNoevo Bump 🙂 If you still want this to be merged, you'll need to make the changes described above (and solve merge conflicts). See PR workflow for details.

[jahd2602]

Duplicate of #35804

[Calinou]

I'll close this due to inactivity. @jahd2602 made a new pull request based on yours with the merge conflicts solved. Thanks for your contribution anyway 🙂