fix(npm): run pre and post tasks if present

[marvinhagemeister]

This PR optionally runs pre and posts tasks from package.json if available.

Fixes #19157

[marvinhagemeister]

Amended a couple more test cases.

[bartlomieju]

Can you add a test that ensure that pre- and post- scripts are not automatically run from deno.json. This feature is fine for compatibility with npm, but I'm not in favor of adding it to Deno's tasks.

[marvinhagemeister]

@bartlomieju the changes in this PR only affect scripts from package.json because they're guarded by an earlier check here https://github.com/denoland/deno/pull/19178/files#diff-25b821ac9f791d719c4d772c106c89752c2da633d53159d615e048990ccc9613L68 Happy to add tests that it doesn't affect tasks from deno.json nonetheless.

[dsherret]

LGTM. Thanks, @marvinhagemeister!