Store refactor: use non-global stores in components

[kegsay]

This is part of a series of PRs aiming to improve stores. This PR focuses on a pattern for passing stores to components in a way that doesn't involve global singletons.

Added a new kind of class:

• Add God object Stores which will hold refs to all known stores and the MatrixClient. This object is NOT a singleton.
• Add StoresContext to hold onto a ref of Stores for use inside components.

StoresContext is created via:

• Create Stores in MatrixChat, assigning the MatrixClient when we have one set. Currently sets the RVS to RoomViewStore.instance.
• Wrap MatrixChats render() function in a StoresContext.Provider so it can be used anywhere.

StoresContext is currently only used in RoomView via the following changes:

• Remove the HOC, which redundantly set mxClient as a prop. We don't need this as RoomView was using the client from this.context.
• Change the type of context accepted from MatrixClientContext to StoresContext.
• Modify alllll the places where this.context is used to interact with the client and suffix .client.
• Modify places where we use RoomViewStore.instance and replace them with this.context.roomViewStore.

This makes RoomView use a non-global instance of RVS.

Checklist

• [ ] Tests written for new code (and old code if feasible)
• [ ] Linter and other CI checks pass
• [ ] Sign-off given on the changes (see CONTRIBUTING.md)

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This change is marked as an internal change (Task), so will not be included in the changelog.

[kegsay]

Agreed the name Stores could be better. I would strongly push for it to be a "general stuff-you-need context" else you end up designing situations where a component may need >1 context which then needs HOC to do and it ends up being more boilerplate for little gain. ReactSDKContext is better but a bit long and probably redundant (given it's a React.Context we needn't mention React, so maybe SDKContext?)

[ara4n]

SDKContext sounds sensible to me, fwiw.

[t3chguy]

Please avoid force-pushing as it makes review harder by not allowing commit-by-commit reviewing

[kegsay]

The force push was done to rebase this PR off develop rather than #9290 - sorry about that. There were no additional code changes.

[t3chguy]

Given we squash merge PRs, you can just merge commit instead of rebasing in most cases

[t3chguy]

Force merging due to regex refactor not needing as much coverage