Bug 1843717 - Don't replace backslashes in the hash of the URL r=necko-reviewers...

Bug 1843717 - Don't replace backslashes in the hash of the URL r=necko-reviewers,kershaw

This bug seems to have existed since bug 249282
The probem was that on windows we wanted to normalize the path of the
file URLs. When doing that bug 249282 also started normalizing the
inputs of relative file URLs, such that it triggers this bug.

When normalizing the input, the normalization should have stopped at the
'#' character. This patch fixes net_NormalizeFileURL to address that.

Since file URLs are only ever parsed with nsStandardURL and this
implementation already normalizes file paths for all special schemes
(file, http, https, etc) calling net_NormalizeFileURL before creating
a file URL is no longer needed, so we can remove the call in
NS_NewURI entirely.

Differential Revision: https://phabricator.services.mozilla.com/D199721