Rename MatrixInMemoryStore to MemoryStore

[jryans]

None of the other store classes use the Matrix prefix, and I find the mismatch
confusing (it leads me to think it might have a different purpose than the
others).

This change removes the prefix from the store for consistency. The old name is
left as an export for existing SDK consumers.

[t3chguy]

This is a breaking change as some things depend on this store. For example: https://github.com/matrix-org/matrix-search/blob/ef289c6e8b3293089a5a422c5664da208f864a52/js_fetcher/index.ts#L167

NVM, I see the double export

[turt2live]

Not to mention all the bots and bridges which use it. A stub class might work, but comments which clear up the confusion might be better.

Edit: I also missed the double export. Can it be made more obvious somehow?

[jryans]

The PR currently preserves exporting the old name for compatibility, as I was expecting issues just like what you've mentioned otherwise.

Does that address these issues?

[jryans]

Can it be made more obvious somehow?

I could add "COMPATIBILITY:" or some other loud string to the comment, maybe?

[turt2live]

It sure reminds me that the project has never been updated for new build practices, but that's a different issue.

I think it should at least get a deprecation notice so we can remove it eventually.

[jryans]

Okay, I have added the deprecation notice as well. (Sorry for tripping everyone's breaking change alarm... 😰)

[turt2live]

Looks like all the instances of it. I assume this has been tested, and that it doesn't cause stuff to explode.

Thanks for deprecating it, and not making it a breaking change from the outset despite everyone's efforts to call you out on it :)

[jryans]

Yes, I've tested that both the old and new exported names are working as expected.