web: Move root routes into a shared constant

[xg-wang]

Summary

This PR moves root routes into a shared constant. Sub routes are not (yet) moved to this top constant.

fixes #20693

Testing

Passed these:

yarn test
yarn all:eslint
yarn prettier-check
yarn all:stylelint
yarn graphql-lint

Note yarn integration-test fails, which also fails on main branch locally.

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[xg-wang]

@natectang CLA signed

[valerybugakov]

Beautiful! Thank you for updating logic in client/web/src/Layout.tsx to use the PageRoutes enum.

Could you update one thing before merging: change enums key casing to CamelCase from UPPER_CASE? We don't have an ESLint rule setup for that yet, but that's the approach used for most of the new functionality in the codebase.

[valerybugakov]

Also, it seems that pulling main into this branch is required to resolve the merge conflict.

[valerybugakov]

@cla-bot check

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[xg-wang]

@valerybugakov thanks for reviewing, I fixed the conflicts and changed the format

[valerybugakov]

change enums key casing to CamelCase from UPPER_CASE

It seems I didn't describe the change above adequately. I should've added an example. Added it to one of the lines changed now.

[valerybugakov]

Excellent, thank you! It's a good start in making our routing more robust.

[ltagliaferri]

Hi @xg-wang, Sourcegraph would love to send you a Hacktoberfest treat, please email us at dev-ed@sourcegraph.com and reference this PR so we can set you up 🎃