chore(core): Refactor core code and remove modifiable Client options

[kitten]

Follow-up to #2611

Summary

This refactors multiple parts of the core package, further reducing size (*.min.mjs) by -100B gzip'd down to nice and round 6kB.

This contains a breaking change (see changeset)

This pull request finally removes options on the Client and only leaves Client.suspense around, which we're using internally and may be needed for some other React functionality.
It removes all other options, like url, fetch, fetchOptions, and so on, which are now constant and not modifiable after the Client has been created.

This further builds on and encourages use of #2610. (setContextExchange). We could further consider deprecating fetchOptions, but I see that as too extreme, really.

Set of changes

• Remove Client.createOperationContext
• Remove on-client options that are modifiable copies of ClientOptions inputs
• Reformat ssrExchange, fetchExchange, fetchOptions, and fetchSource slightly
• Reference Symbol.asyncIterator directly in fetchSource as symbols are in our ES2015 scope
• Reformat CombinedError code
• Reformat and refactor maskTypename

[changeset-bot]

🦋 Changeset detected

Latest commit: 3844031

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 5 packages

Name	Type
@urql/core	Major
@urql/preact	Patch
urql	Patch
@urql/svelte	Patch
@urql/vue	Patch

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