Move over Sorbet stdlib types for the cmath gem

[Tom-Bonnike]

Sorbet is soon going to stop shipping with types for a few core gems that aren’t bundled with ruby anymore since v2.7.0, see sorbet/sorbet#8377.
cmath is one of these gems, and there was some type annotations for it in the Sorbet repo. I’m just moving them over here instead. There seems to have been no update to the cmath gem since it was made a non-default gem in Ruby 2.7.0, but I still manually checked and the types look correct.

Type of Change

• Add RBI for a new gem
• Modify RBI for an existing gem
• Other:

Changes

• Gem name: cmath
• Gem version: 1.0.0
• Gem source: https://github.com/ruby/cmath/blob/master/lib/cmath.rb
• Gem API doc: https://github.com/ruby/cmath
• Tapioca version: Latest
• Sorbet version: Latest

[Tom-Bonnike]

I have signed the CLA!

[KaanOzkan]

This is failing CI for now but the duplication should be fine as users upgrade their Sorbet version. I'd like to keep the CI green though. Is it okay if this PR waits until Sorbet removal is merged and we bump the Sorbet version used in tests?

[Tom-Bonnike]

I guess that makes sense — although we should aim for as little time as possible between the two merges, then.