feat(add): Add npm packages to package.json if present (#25477)

Closes https://github.com/denoland/deno/issues/25321

Ended up being a larger refactoring, since we're now juggling
(potentially) two config files in the same `add`, instead of choosing
one. I don't love the shape of the code, but I think it's good enough

Some smaller side improvements:
- `deno remove` supports `jsonc`
- `deno install --dev` will be a really simple change
- if `deno remove` removes the last import/dependency in the
`imports`/`dependencies`/`devDependencies` field, it removes the field
instead of leaving an empty object

1 files changed, 3 insertions, 0 deletions

diff --git a/tests/specs/remove/basic/__test__.jsonc b/tests/specs/remove/basic/__test__.jsonc
index 2f4d82c88..495496b5c 100644
--- a/tests/specs/remove/basic/__test__.jsonc
+++ b/tests/specs/remove/basic/__test__.jsonc
@@ -12,5 +12,8 @@
   }, {
     "args": ["eval", "console.log(Deno.readTextFileSync('deno.lock').trim())"],
     "output": "remove_lock.out"
+  }, {
+    "args": ["eval", "console.log(Deno.readTextFileSync('deno.json').trim())"],
+    "output": "{\n}\n"
   }]
 }