[fela-plugin-rtl] Ability to set default direction

[robinweser]

Description

Adds the ability to set a default direction when using fela-plugin-rtl in order to use the theme.direction approach for conditional rtl transformation.

Packages

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• fela-plugin-rtl

Versioning

Patch (as this should have already been part of the last minor)

Checklist

Quality Assurance

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• The code was formatted using Prettier (yarn run format)
• The code has no linting errors (yarn run lint)
• All tests are passing (yarn run test)
• There are no flow-type errors (yarn run flow)

Changes

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• Tests have been added/updated
• Documentation has been added/updated
• My changes have proper flow-types