Simplify implementation of internal FFI function intercalate in Data.Show.Generic

[cdepillabout]

Description of the change

The Data.Show and Data.Show.Generic modules both use an internal FFI helper function intercalate. It was called join in Data.Show.

This PR does the following:

• Simplifies the implementation in Data.Show.Generic.intercalate. This now matches the same (simple) implementation from Data.Show.
• Renames the function in Data.Show to be intercalate. My reasoning is that the function should be named the same thing in both Data.Show and Data.Show.Generic. I thought intercalate would be easier to understand for a PureScriter, since intercalate is already used in modules like Data.Foldable. (Alternatively, intercalate could be renamed join in both modules, since join is the name of the underlying FFI function. I decided against this since join has a different meaning in PureScript. I thought intercalate was easier to understand.)

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Checklist:

• Added the change to the changelog's "Unreleased" section with a reference to this PR (e.g. "- Made a change (#0000)")
• Linked any existing issues or proposals that this pull request should close
• Updated or added relevant documentation
• Added a test for the contribution (if applicable)

[cdepillabout]

I didn't add a changelog entry for this, since this change shouldn't be visible to any users.

[thomashoneyman]

@cdepillabout This can be added to the CHANGELOG under the "Other improvements" section if you would like, but it isn't necessary if you don't want to.

[JordanMartinez]

Perhaps a changelog should be added for other backend maintainers because the function name is changing from join to intercalate?

[cdepillabout]

Thanks for the review.

I've added a CHANGELOG entry for this change. Hopefully this should be good to merge now.

[JordanMartinez]

I'd like to merge this, but I'll clarify how this change affects non-JS backends before doing so. While this isn't a breaking change for the JS backend, I wonder if it is for non-JS backends.

[JordanMartinez]

Per Nate, this counts as a breaking change for non-JS backends. So, we shouldn't merge it until we're making breaking changes in general.

I've added that label here.

[JordanMartinez]

🏓 @thomashoneyman