This change adds a 'db' attribute to the `Bugzilla::DB::Schema` class.
In two places (`get_empty_schema` and `deserialize_abstract`) the invocant
argument was called `$class` but was never actually a class. Those were renamed
to `$self`. It was fortunate that they were always objects because otherwise it
would have been more difficult to ensure a `db` is always present.

Bugzilla::DB::Schema->new() was both a normal constructor and also a
class-loading factory method. It is simpler to just do the class loading at the
call-site (in Bugzilla::DB::_bz_schema).

It's not very likely extensions relied on this behavior so this should be a good
change.

* use base to make merging with bmo easier

* Revert "Bug 1497042 - Enclose table names in CREATE queries"

This reverts commit 62d5637a.

* refactor Bugzilla::DB to not subclass DBI

* use DBIx::Connector to manage database connections

* Ensure we always call DBIx::Connector->dbh before any DBI method

The code didn't allow a way of doing this without a lot of work.

So I had to take the following approach:
The 'dbh' attribute is now a method that delegates to DBIx::Connector's dbh
method. Per the docs, ->dbh() "Returns the connection's database handle. It will
use a an existing handle if there is one, if the process has not been forked or
a new thread spawned, and if the database is pingable. Otherwise, it will
instantiate, cache, and return a new handle."

Then there is the matter of the 'handles' on dbh. I've used Package::Stash to
insert proxy methods into the class when it is loaded.

* Bug 1328659 - Add support for utf8=utf8mb4 (switches to dynamic/compressed row format, and changes charset to utf8mb4)

* add deps

* add prepare_cached to the list of delegated methods.

This was added in bug 340160

* improve the migration to compressed/dynamic rows, skip views

* add missing semicolon

* remove pre-utf8mb4 emoji support

* fix small issue

* add debugging fatal error

blame jeff

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Bug 1137669: 003safesys.t doesn't test any file due to a missing -T argument (and broken syntax in Support::Systemexec)
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Bug 880282: Replace |FILTER no_break| by |class="nowrap"| to prevent dashes (U+002D) from being replaced by non-breaking hyphens/dashes (U+2011)
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Bug 963120 - allow extensions to document themselves, and build result into docs. r=LpSolit, a=justdave.

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Bug 770073 - Hardcode "Bugzilla" in templates when it's not related to a specific Bugzilla installation
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https://bugzilla.mozilla.org/show_bug.cgi?id=714074

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Bug 680131: Replace the MPL 1.1 license by the MPL 2.0 one in all files, and add it to files which miss one
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