Fix issues in require/init when dealing with virtual packages which do not exist

[Seldaek]

Fixes #10489

• composer require psr/log-implementation:* now works
• composer require psr/log-implementation (without constraint) prompts for a version:

$ c req psr/log-implementation
Package "psr/log-implementation" does not exist but is provided by 124 packages. Which version constraint would you like to use? [*] ^2
Using version ^2 for psr/log-implementation
./composer.json has been updated
Running composer update psr/log-implementation

• composer init when searching for virtual packages also checks for providers and if one is found the provided name is added to the list of matches from the package search (previously only xxnoobmanxx/psrlogger was suggested here)

Define your dependencies.


Would you like to define your dependencies (require) interactively [yes]? Search for a package:
Would you like to define your dev dependencies (require-dev) interactively [yes]?
Search for a package: psr/log-implementation

Found 2 packages matching psr/log-implementation

   [0] psr/log-implementation
   [1] xxnoobmanxx/psrlogger

Enter package # to add, or the complete package name if it is not listed:

cc @dzuelke

[dzuelke]

Amazing. Thanks for the work; I've run it through my integration tests (code used manual composer.json update and then composer update … before), and it looks like this does the job splendidly!