Red Squigglies in Editor show TS types as errors

[e111077]

When writing types in the editor in TS files, it shows a red squiggly under the type

[e111077]

Doing some weirdo things

[aomarks]

The JSDoc types can only be used inside documentation comments is actually a legit syntax error because the ! should be on the property name instead of the type (inputEl!: HTMLInputElement). Pretty confusing tsc error, but not specific to playground.

The Property 'dispatchEvent' does not exist on type 'CounterButton'. error is because we don't have the LitElement typings loading in yet (tracking at #119). We shouldn't show it for now though --- adding that error code to the list of temporary exclusions in #122.