net/url, net/http/httputil: accept invalid percent encodings

net/url, net/http/httputil: accept invalid percent encodings

Per https://url.spec.whatwg.org/#percent-encoded-bytes an invalid
percent encoding should be handled as ordinary text.

Fixes #56732

Change-Id: Ib0259dfd704922905289eebaacbf722e28f6d636
Reviewed-on: https://go-review.googlesource.com/c/go/+/450375
Run-TryBot: Ian Lance Taylor <iant@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
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