[Documentation] recommend using typePolicies instead of writeQuery/writeFragment whenever possible

[jedwards1211]

I'm happy to make a PR for this eventually, just bringing this up because I don't have time atm...

I went years without knowing about cacheRedirects and thinking writeQuery/writeFragment was the only way to accomplish what I needed. The docs don't raise enough awareness of this feature.

This is still a problem in v3 since the Local State Management docs don't mention typePolicies. We should add a note above the Updating local state section, something like

In many cases, using typePolicies to customize cache reads is easier and more maintainable than manually reading or writing local state. For example, after querying a list of users, if you want a query for one of those users by id to be served from the cache, this is much easier to accomplish using typePolicies than by doing writeQuery for each user in the list.

[hwillson]

Thanks @jedwards1211 - we're currently working on overhauling all docs sections for the upcoming AC3 launch. These changes should start to appear in PR's later this week.

[hwillson]

Docs changes are happening in #6429 and can be tracked there, so I'll close this off. Thanks!