Add option for deno add to update package.json for npm packages

[redabacha]

currently running deno add will only update the deno configuration imports field however this isn't always desirable. for example when using typescript directly for type checking in a project rather than deno's type checker, intellisense imports will not work unless they're specified in the package.json.

with npm packages in deno.jsonc imports:

with npm packages in package.json dependencies:

[redabacha]

i've noticed that if the package.json is gone entirely, then it also seems to work as expected. i'm not familiar with typescript/vscode internals but i guess it's falling back to checking the node_modules folder if the package.json is missing?

[dsherret]

We're going to update it for Deno 2.0 to add npm dependencies to the package.json if it exists. Otherwise it will continue to add to the deno.json.