Draft: Doc: Encourage consistency regarding quotes in the same file

What does this MR do?

This MR clarifies the development guidelines that we should not mix double and single quotes in the same file.

Addresses comments like:

• #198046 (comment 274719269)
• #198046 (comment 1096459241)

If we cannot agree to be consistent on a global level (due to "sheer amount work to rectify") we could try to be consistent on a per-file basis.

Potential cop follow-up

We could create a cop to check the consistency of quote style in the same file.

Related issues

Follow-up of !97632 (merged).

Refs #198046

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