example config to be propagated across packages

[alexforsyth]

Issue #, if available:

Description of changes:

Experimental PR to show how we'd implement a root tsconfig. This works properly for the abort controller package

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[alexforsyth]

Key points:

1. There is now a root ts-config, we'll put all the common ts options there.
2. Individual packages no longer have a tsconfig. This is because vscode looks for the nearest tsconfig in the tree. By removing it, vscode jumps to using the root tscofig and provides all sorts of awesome goodies like paths and automatically highlighting places that do not adhere to the root tsconfig options.
3. Individual packages still have a tsconfig.test.json. This inherits from the root tsconfig. Used by lerna when we want to build tsc.

[codecov-commenter]

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[trivikr]

target should be browser TSConfig target, as that's usually the lower version of ECMAScript.

[trivikr]

decided to exclude lib, as it's overridden in individual clients

[github-actions]

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