Support draw rounded rectangles with varying corners.

[GPrimola]

Description

This PR extends the already existent Scenic.Script.draw_rounded_rectangle/5 functions to 3 others:

• Scenic.Script.draw_rounded_rectangle/6
• Scenic.Script.draw_rounded_rectangle/7
• Scenic.Script.draw_rounded_rectangle/8

Those extra arguments can be used to draw a rounded rectangle with varying corners radii, and it was done having in mind the HTML <canvas> spec for rounded rectangle while keeping the already existing behavior of rounded rectangle on Scenic.

This functionality was implemented using the already included function nvgRoundedRectVarying on the NanoVG's version Scenic relies on, so there's no need to update any dep's version.

This PR depends on and relates to ScenicFramework/scenic_driver_local#17.

This PR introduces no breaking changes once it doesn't change neither the interface nor the behaviour of the previous existing Scenic.Script.draw_rounded_rectangle/5.
And while it depends on ScenicFramework/scenic_driver_local#17, it won't break without it. Instead of breaking, scenic_driver_local/c_src/script.c will only emit a log warning that the operation 0x0C (draw_rrectv on Scenic) doesn't exist.

Motivation and Context

The motivation behind this PR is for Scenic.Script be more compatible with HTML specs.

Types of changes

• Bug fix (a non-breaking change which fixes an issue)
• New feature (a non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to
  not work as expected)
• Improvement/refactoring (non-breaking change that doesn't add any feature
  but make things better)

Checklist

• Check other PRs and make sure that the changes are not done yet.
• The PR title is no longer than 64 characters.

[crertel]

Otherwise, super neat work!

[GPrimola]

ok

[GPrimola]

Hi @crertel, can you take a look on this again? :)

Many thanks!

[GPrimola]

Hey @crertel,
on #290 (review) you added a change request.
After that I've tackled some stuff. Could you check again if the changes you requested have been tackled?

Thanks! :D

[crertel]

The other half of this is handled in ScenicFramework/scenic_driver_local#67 .