Automatically fix Deno imports when using a val as a module

[RLesser]

Within val town, using npm: style imports works well, but when importing the val as a module this causes it to break. But switching to an explicit esm package import instead causes typing to fail. We should be able to use npm: in the val and have it auto replace with the module url when importing as a module

[stevekrouse]

Original Discord discussion: https://discord.com/channels/1020432421243592714/1209278932189315163

[neverstew]

Big yes from me!

[stevekrouse]

I added a userspace label to this because in theory this feature could be built as a CDN on val town or another site in userspace - ie outside of val town the company - at least to start