…nBeEnabled to canBeDisabled (fabpot)

This PR was squashed before being merged into the 3.3-dev branch (closes #21196).

Discussion
----------

[FrameworkBundle] changed some default configs from canBeEnabled to canBeDisabled

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a

FrameworkBundle configuration is currently "optimized" for when a project
depends on symfony/symfony (which is the vast majority of Symfony projects out
there as that's how Symfony Standard Edition is set up). As all components are
always available, features (forms, validation, translation, serializer, ...)
are disabled by default in FrameworkBundle's configuration (`canBeEnabled`) and
developers must enable them when they need them (that was done mainly for
performance reasons).

That's annoying as it means one configuration step before being able to use
forms for the first time (or validation, or serialization, or translation, ...).

To make features auto-configurable and make the framework a bit more
user-friendly (that's where I think I need to invoke DX :), I'd like Symfony 4
to work in a different way. Instead of relying on symfony/symfony, I want
people to install only the components/bundles they need. In that scenario, we
can auto-configure Symfony FrameworkBundle based on the available components.
If you add symfony/form as a dependency, then it makes sense to automatically
enable the feature in framework bundle (with the possibility to disable it if
needed thanks to `canBeDisabled`).

Let's recap:

 * Before:

   * You want to use forms; you have symfony/symfony, so nothing to install;

   * Using forms does not work out of the box though; you need to know that you
     have to edit `app/config/config.yml` to explicitly enable forms;

   * Forms work!

 * After:

   * You want to use forms so you install symfony/form (like for any other
     packages out there; want to use Twig for templating, install twig/twig);

   * But for Symfony components, there are no other steps; forms are
     auto-configured just because you installed the dependency, go work now!

In a way, it makes handling/installing/configuring Symfony components no
different than doing the same for a third party package. That's about relying
even more on Composer and less on configuration. Symfony components have the
extra benefit of being auto-configured via FrameworkBundle. That's not the case
for other third-party packages/bundles, but for those who attended SymfonyCon
Berlin, you know that this is coming soon via Symfony Flex.

That's even more interesting for forms as CSRF protection needs an extra knob
to be turned on currently. With the new way, just install the CSRF security
component. An again, you still have the possibility to turn it off if you want
to.

Anyway, this PR gives us the flexibility to do both: when using
symfony/symfony, everything works as before, if you are using
symfony/framework-bundle, then auto-configuration based on the installed
packages is automatically activated.

This also brings consistency as this behavior is already what we've done for
the Doctrine Annotation library in 3.2.

Last, but not the least, with all the work currently done on the container
lazyness for Symfony 3.3, concerns about performance are less important than
before, so having components auto-enabled when installed should not be a big
deal. We might even go one step further and remove enabling/disabling for
ESI/SSI/fragments/... And whenever we create an independent Session component,
we will be able to do the same with the session configuration. The astute
reader might have noticed that I haven't talked about the templating
configuration, but as the component will be deprecated in 3.3, I prefer to keep
its activation explicit.

In terms of BC, the only change is for people using symfony/framework-bundle
with some packages that were installed but not enabled in the config. I would
say that this should be pretty rare and anyway, the only consequence is a small
performance hit which can be easily offset by explicitly disabling the config.

That's all folks!

Commits
-------

ef80873 [FrameworkBundle] changed some default configs from canBeEnabled to canBeDisabled
98ce21a [FrameworkBundle] changed the default value of annotation setting based on the existence of Doctrine Annotations

This PR was merged into the 3.3-dev branch.

Discussion
----------

[TwigBundle] Disable form in tests

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a

Tests are broken with high deps due to the changes made in #21196

> Symfony\Bundle\TwigBundle\Tests\NoTemplatingEntryTest::test
Symfony\Component\DependencyInjection\Exception\LogicException: Form support cannot be enabled as the Translation component is not installed.

> Symfony\Bundle\TwigBundle\Tests\NoTemplatingEntryTest::test
Symfony\Component\DependencyInjection\Exception\LogicException: The Validator component is required to use the Form component.

This will fix them.

Commits
-------

2a279b9 [TwigBundle] Disable form in tests