This is to prepare for custom search engines. If we use AK::format, it
would be trivial for a user (or bad actor) to come up with a template
search engine URL that ultimately crashes the browser due to internal
assertions in AK::format. For example:
https://example.com/crash={1}
Rather than coming up with a complicated pre-format validator, let's
just not use AK::format. Custom URLs will signify their template query
parameters with "%s". So we can do the same with our built-in engines.
When it comes time to format the URL, we will do a simple string
replacement.
The current helpers assume that a valid URL is a full URL (i.e. contains
the "://" separator between the scheme and domain). This isn't true, as
"file:" alone is parsed as a valid URL.
We must also avoid simply searching for the parsed public suffix in the
original URL string. For example, "com" is a public suffix. If we search
for that in the URL "com.com", we will think the public suffix starts at
index 0.
