Add large type to gel-foundations

[sareh]

Part of #1508

Overall change: Add additional GEL Type sizes for large contexts (Atlas, Elephant, Imperial, Royal, Foolscap) Sizes here: https://www.bbc.co.uk/gel/guidelines/typography#additional-type-sizes-for-larger-contexts

UX context: When pairing with UX, it was decided that to start with all non-Latin font-sizes and line heights will initially be the same as those for Latin. Then they will stress-test these types with different scripts and where relevant ask for changes in a separate issue.

Code changes:

• Add additional GEL Type sizes for large contexts (Atlas, Elephant, Imperial, Royal, Foolscap) to the scripts
• Add the methods getAtlas etc. which can be used by others within components.

Testing Note: this first PR does not update Storybook with the typography! http://localhost:8180/?path=/story/typography--canon this needs to be carried out with an update to psammead-styles in a separate PR after this gel-foundations change has been merged. There will be a second PR for this issue #1508 to be complete.

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• I have assigned myself to this PR and the corresponding issues
• Tests added for new features
• Test engineer approval

[DenisHdz]

LGTM, but I have been comparing all the values with the ones UX added in the spreadsheet and I found several differences.

[Bopchy]

Other than Dennis' comment, looks good - LGTM

[sareh]

@DenisBBC Thanks for the detailed review with all of your suggestions, Denis!
However, having checked with UX, they'd like for us to use the Latin type sizes until they have been fully stress-tested for the other scripts and to then add the corrected type sizes at that point.

[DenisHdz]

Thank you for confirming this 👍

[sareh]

This has been UX reviewed and approved.

[paruchurisilpa]

Moving this to Ready for merge without testing as this would be tested once #1508 is done