Improve TypeScript generated code (fixes and improvements)

[drogus]

Description of Changes

This is a set of changes improving various parts of TypeScript autogen:

• properly map u64 and i64 values to BigInt
• change the way we handle client db in classes, which is needed for allowing to run multiple SpacetimeDB clients in TypeScript. The new API will allow to do sth like User.with(client).onInsert(...)
• change in how reducers and tables are registered - instead of doing it automagically on import, we will now require explicit call to SpacetimeDBClient.registerReducers or .registerTables. The problem with doing it automagically is that it will sometimes fail. Node will filter out any imports that are unused, so if you import a table without actually using the class constant, but you do a subscribe, it would result in an error. With explicit include it's no longer a problem
• now we will also export constants and/or functions for enum variants. So far using enum variants was cumbersome, cause given a reducer like foo(user_type: UserType) where UserType is an enum, in javascript you would have to do sth like FooReducer.call({ tag: "Admin", value: undefined }), which requires you to know how sum types are constructed in TypeScript. With the changes from the PR you can now do FooReducer.call(UserType.Admin). For an enum variant with value it would be sth like AnEnum.VariantA("a value") which will return { tag: "VariantA", value: "a value" }
• I fixed a case where we converted __identity_bytes to camel case, which resulted in an error
• changed the API for how reducer callbacks are defined. instead of providing an args: any[] array we now list all of the values with proper types. So for example given an add(u64, u64) reducer the callback signature for a callback would be sth like (reducerEvent: ReducerEvent, a: BigInt, b: BigInt)

API and ABI breaking changes

These changes will break the TypeScript SDK, so a new release will be needed when this is released.

Expected complexity level and risk

I think it's a 2, it's not overly complex and it will actually lower some of the complexity in the SDK (for example by being more explicit with registering reducers and tables)

[gefjon]

I like all these changes. I'd like to see a corresponding docs PR to update the SDK ref (and quickstart, if necessary) to reflect the new interface. I'd especially like the docs on Table.with to be very clear about whether that mutates global state (I believe it doesn't), with an example that describes the behavior of:

MyTable.onInsert(someCallback)

MyTable.with(conn).onInsert(otherCallback)

MyTable.onInsert(thirdCallback)

I also notice that the corresponding TypeScript SDK PR doesn't update examples/quickstart. The main way I'll be convinced that this is ready for the big time is when the quickstart client builds and runs.

[drogus]

@gefjon sorry for a late reply and thanks a lot for a review!

I updated the quickstart guide in the SDK PR, but there are almost no changes to make it work. The .with interface is only required if you want to create multiple clients, the default behaviour will be to use the first instantiated client. I will add more docs on the with method (like in the code + ref), but I don't think we should advertise it too much, like I would definitely not use it in the quickstart guide. It's only for unusual situations where you need to connect to multiple instances of SpacetimeDB or when you need multiple clients for the same database for some reason.

[drogus]

So the only changes in the actual app code for quickstart is this diff, ie. adding registerTables and regusterReducers calls