Deno.bundle() should accept the compiler flag `importsNotUsedAsValues`

[timonson]

This tsc compiler flag was implemented in TypeScript 3.8. You can find the merged PR here: microsoft/TypeScript#35200

This flag takes 3 different values:

• remove: this is today’s behavior of dropping these imports. It’s going to continue to be the default, and is a non-breaking change.
• preserve: this preserves all imports whose values are never used. This can cause imports/side-effects to be preserved.
• error: this preserves all imports (the same as the preserve option), but will error when a value import is only used as a type. This might be useful if you want to ensure no values are being accidentally imported, but still make side-effect imports explicit.

It would be very helpful for Web Components and other stuff.

[bartlomieju]

Ref #6456

CC @kitsonk

[kitsonk]

@bartlomieju this is different... It just needs to be added to the compiler APIs Compiler Options and converted to the right internal TypeScript type.