Add globalStorage/didChange agent endpoint

[pkukielka]

Test plan

N/A. It will be needed for sourcegraph/jetbrains#2382

Protocol files need to be regenerated but this have to be fixed and merged first.

[dominiccooney]

Let's not do it this way. VSCode globalState is shared, and there's no notifications when other agents are editing it. We should build the notification we need at the semantic level in the extension and use that, instead of exciting some action every time global state changes.

What specifically are we using this for on the JetBrains side?

[dominiccooney]

I think we need to build the notification we need at the semantic level, instead of adding a notification on global state writes. Global state doesn't have this kind of notification for other concurrent editors, and I doubt we need notice every time someone writes anything into global state.