Breaking: #108084 - Allow rootless paths in URI implementation 

Description 

Previously, the TYPO3 implementation of \UriInterface always prefixed rootless paths (paths without a preceding slash) with a slash. With this normalization in place, it was impossible to represent rootless paths. This has now changed so that a slash is only prepended to the path when an authority (host name) is present.

use TYPO3\CMS\Core\Http\Uri;

$uri = new Uri('rootless/path/');
$uriAsString = (string)$uri;
// before: /rootless/path/
// after: rootless/path/

// Same behavior with authority
$uri = (new Uri('https://example.com'))->withPath('rootless/path/');
$uriAsString = (string)$uri;
// before: https://example.com/rootless/path/
// after: https://example.com/rootless/path/

// Colon in first path segment
$uri = new Uri('rootless:path/to/resource');
$uriAsString = (string)$uri;
// before: /rootless:path/to/resource/
// after: ./rootless:path/to/resource/

Impact 

Regarding top level TYPO3 API and functionality, nothing has changed. Required TYPO3 code has been adapted.

Third party code that uses the Uri class directly will get different results when representing rootless paths without authority. Code that relied on the normalization done by TYPO3 before is likely to break.

Since TYPO3 is always dealing with absolute paths, due to URL rewriting in the backend and the frontend, it is unlikely that much third party code relies on relative paths, so the impact is expected to be low.

Affected installations 

Third party code that is using the Uri class directly and that is representing rootless paths without authority.