Miter limit should be parameter with default value, not hardcoded.

[ghmart]

Godot version:
3.2

Issue description:
When using offset_polygon_2d with JOIN_MITER join type it cuts nesessary geometry sometimes:

On the left is what is needed. On the right is what offsetting polygon gives.

Please, add this! Original library allows miter limit to be set.

[akien-mga]

I think that's what #29758 does (@Xrayez)

[ghmart]

Yes, that's what #29758 does. My apologies. Thought my question on forums were missed and made this issue.

[Xrayez]

@ghmart Yeah, no problem, it just makes it more clear what should be done.