Implement parsing text contained in <a> tags enabling users to also
include links in their comment replies posted using inbound email.
Historically, we were holding back on this for two reasons:
* It makes parsing email more complex and fragile
* Spammers can use this to post spammy links on Gerrit
Inbound email is live on gerrit-review.googlesource.com for almost a
year now and we have seen little to no spam. It is enabled on the
majority of Gerrit sites hosted at Google and we have only seen a single
instance of spammy comments. Therefore, the second concern is gone.
This commit adapts the inbound HTML parser and makes some parts of it
more strict to mitigate the first concern. It also adapts some of the
tests as the HTML was incorrect which is surfaced by the enforcement of
stricter parsing rules.
We parse the text contained in the <a> tag, because we expect users to
just copy and paste a link into their email response and have their
email client turn it into a link automatically rather than have them
mingle with a word that they turn into a link manually.
Bug: Issue 7553
Change-Id: I70ca1977554d9f218280abe188d670ea41daa1f4
78fe705caa