Description:
------------
parse_url looses the leading '/' character in paths with single-letter Windows drive letters.

According to the RFC8089 Section 2[1]:

> The generic syntax in [RFC3986] includes "path" and "authority"
  components, for each of which only a subset is used in the definition
  of the file URI scheme.  The relevant subset of "path" is "path-
  absolute"

'path-absolute' in RFC3986 is defined as beginning with a '/' character.

There's also a requirement in RFC3986 section 3.3 [2], that

> If a URI contains an authority component, then the path component
  must either be empty or begin with a slash ("/") character.

For file:///c:/ URL the authority component is present but empty, which implies 'localhost'. Thus the 'path' component must begin with the '/' character.

Other popular languages like Java or JavaScript preserve the leading slash character as well.

[1] https://datatracker.ietf.org/doc/html/rfc8089#section-2
[2] https://datatracker.ietf.org/doc/html/rfc3986#section-3.3


Test script:
---------------
var_dump( parse_url( 'file:///c:/' ) );

Expected result:
----------------
array(2) {
  ["scheme"]=>
  string(4) "file"
  ["path"]=>
  string(4) "/c:/"
}

Actual result:
--------------
array(2) {
  ["scheme"]=>
  string(4) "file"
  ["path"]=>
  string(3) "c:/"
}