Merge remote-tracking branch 'upstream/2.14.x' into 1.x

* upstream/2.14.x:
  Since `InstalledVersions` changed API completely in `composer-plugin-api:^2.1.0`, we need to cast results to `(string)`
  Upgraded to `composer-runtime-api:^2.1.0`
  Removed redundant check for the existence of `InstalledVersions::getAllRawData()`
  Dropped compatibility with `composer/composer:<2.0.14`
  Don't call deprecated InstalledVersions::getRawData()

Author: nicolas-grekas