Rule Request: Enforce `Double` for function arguments instead of `CGFloat`

New Issue Checklist

• Updated SwiftLint to the latest version
• I searched for existing GitHub issues

New rule request

1. Why should this rule be added? Share links to existing discussion about what the community thinks about this.

I prefer to only use Double for floats in my own functions, for consistency and ease of use, never CGFloat. I only support 64-bit systems, so CGFloat has no practical benefit for me. However, I often get PRs on my open source projects where they use CGFloat. Would be nice to be able to enforce using Double.

2. Provide several examples of what would and wouldn't trigger violations.

Would trigger:

func foo(number: CGFloat) {}

Would not trigger:

func foo(number: Double) {}

3. Should the rule be configurable, if so what parameters should be configurable?

No

4. Should the rule be opt-in or enabled by default? Why?
   See README.md for guidelines on when to mark a rule as opt-in.

Opt-in

Start with README.md's opt-in rules guidance and review how the requested rule should fit SwiftLint's rule conventions. Use the examples in the issue as the initial behavior checks: a function argument typed as CGFloat should trigger, while one typed as Double should not; the rule should be opt-in and have no configuration.