[docs] Add missing routeId slashes

[brunnerh]

Implementation was changed in #7338
Documentation was not updated everywhere.

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[gtm-nayan]

Thanks, the JSDoc comments for routeId in Page and RequestEvent also need to be updated in types/index.d.ts. @brunnerh could you get those as well in this PR?

[brunnerh]

Should be fixed.

[Rich-Harris]

thank you!