The recipe unpacker should explicitly write the unpacked version of the recipe into its composer.json

Problem/Motivation

The recipe unpacker is, in effect, a version lock. When you unpack a recipe and remove it from Composer's awareness, you are pinning it to that specific version.

That's all well and good, but it means we have no way to interrogate Composer to ask which version of the recipe was installed -- which is very much necessary for, say, downloading the correct translation of the recipe.

Normally you'd use the version field in composer.json for that, but there is no guarantee that will be set, because Composer can and does infer versions from things like Git tags and such.

Proposed resolution

The recipe unpacker should alter the unpacked recipe's composer.json file and write the version field explicitly. It has access to the version because it has access to the PackageInterface object and its getPrettyVersion() method.