docs(core): Add TSDocs annotations to @urql/core exported APIs

[kitten]

Summary

This adds TSDoc annotations to all exported APIs.
Generally, the style guide followed is:

• The short description will not contain links
• @param and @returns tags are generally added and contain links
• The remarks will contain further functionality if this isn't obvious from @param or @returns tags
• All notes to implementors/users are marked further with Hint:
• @see links are added to refer to important, otherwise not linked, parts of the TSDocs or web links
• Examples are only added when they illustrate a non-obvious usage pattern
• @throws is added if it's not obvious that an API can explicitly throw an error

This is the first PR that makes use of the build changes from #2956, which bundles all d.ts typings files, which gives a better TSDocs experience.

Since we weren't sure whether slowly adding TSDocs to all our packages is worthwhile (it’s extremely time intensive) we ran polls to validate it:

• https://twitter.com/_philpl/status/1625563558242095120
• https://toot.cafe/@philpl/109864524217575806

At the time of creation of this PR,

• 42.4% voted that detailed TSDocs have a highly positive impact
• and 39.4% voted that it had a medium (situational impact)
• the minority voted that it only has a low impact

Set of changes

• Add TSDocs to all @urql/core exports
• Hide accidentally exposed fallbackExchangeIO export (not considered breaking/minor since it's unlikely to be used and was never meant to be exposed)