feat(add): strip package subpath when adding a package (#25419)

These now works:
```
$ deno add @std/dotenv/load
$ deno add npm:preact/hooks
```
Previously we were erroring out, because this is a "package reference"
including
a subpath.

Closes https://github.com/denoland/deno/issues/25385

---------

Signed-off-by: Bartek Iwańczuk <biwanczuk@gmail.com>
Co-authored-by: David Sherret <dsherret@users.noreply.github.com>

1 files changed, 19 insertions, 0 deletions

diff --git a/tests/specs/add/add_with_subpath/__test__.jsonc b/tests/specs/add/add_with_subpath/__test__.jsonc
new file mode 100644
index 000000000..b051bd265
--- /dev/null
+++ b/tests/specs/add/add_with_subpath/__test__.jsonc
@@ -0,0 +1,19 @@
+{
+  "tempDir": true,
+  "steps": [
+    {
+      "args": "add @std/testing/bdd npm:preact/hooks",
+      "output": "add.out"
+    },
+    {
+      "args": "add @std/testing/bdd@1 npm:preact/hooks@10",
+      "output": "wrong_constraint_jsr.out",
+      "exitCode": 1
+    },
+    {
+      "args": "add npm:preact/hooks@10",
+      "output": "wrong_constraint_npm.out",
+      "exitCode": 1
+    }
+  ]
+}