build: mirror nitro and nitropack npm packages

[pi0]

TLDR

This PR allows a way to use nitro or nitropack as a dependency and import the same.

Context

With access to nitro npm package (thanks to @jgermade and @danielroe) we can adopt using a shorter name across.

I had some doubts about this from #1362 mainly because we cannot use @nitro/ namespace in npm but with structure overhaul (#2473) and adoption of subpath exports, this is no longer a concern + usage of subpaths gives much more reasons that more end-users would benefit from explicit imports in their codebase rather than usages of a zero-dep CLI utility.

Approach

Adoption is tricky. We have a lot of current users that depend on nitropack as canonical and nitro can be only versioned for >3 to avoid conflict with the previous state.

This PR:

• Add builder configuration to have interchangeable import from nitro or nitropack
• Adds an automated script to generate a virtual mirror package

The virtual mirror package does not copy but reexports subpaths. This is to ensure in mixed scenarios, we don't duplicate bundle and install sizes.

Mirror dependency

The mirror package needs to have a dependency on the main package. Using peerDependencies is ideal because can help to dedup, but it turns out in cases like using npm: alias package managers show strange behavior and won't install! So it main package is in the dependencies of the mirror package.

Nitro 2.x (current)

Nitro 2.x, will use nitropack as canonical as before to avoid any changes but only supports nitro/ subpath import aliases that will redirect to nitropack/ for forward compatibility.

We release nitro@2.x.y-nitropack-mirror (with 2.x tag) and nitro-nightly@2-compat for forward compatibility.

Nitro 3.x (next)

Nitro 3.x, will use nitro as canonical and redirect nitropack/ subpath imports.

We release nitropack@3.x.y-nitro-mirror (with the latest tag) and nitropack-nightly@3.x.y-nitro-mirror for backward compatibility.

TODO

• (postponed) type augmentations should work via nitro/nitropack/nitro/types and nitropack/types regardless of canonical (nitro{pack}/types)