fix(tree): not allowing horizontal overflow

[crisbeto]

The way the tree styles were set up initially means that the tree element can't cause its parent to overflow. Given that the tree can have a lot of nesting, this is bound to happen with deeper trees. These changes remove the default overflow: hidden since it doesn't seem to be doing much.

Fixes #18182.

[crisbeto]

Caretaker note: this has the potential to break screenshot tests. We should run a presubmit and figure out whether we still want to do it based on the results. If it's too breaky we can recommend to people to override our styles.

[gubo]

i could not affect overflow:hidden on the right element or at the right time, trying combinations of mat-tree, ng-deep, etc ... can you advise on how to affect this style in the above test project ?
in general, this is the main failure/shortcoming of angular material ... it is too hard / sometimes not possible, and there is no consistent way, to affect styles on material components ... especially when not using ng-deep nor ViewEncapsulation.NONE ...
is there a way to the material library could be made to accept styling in a consistent way ?
in the meantime, i am just dropping down to cdk-tree and not using mat-tree ...
thanks much :)

[jelbourn]

LGTM

[angular-automatic-lock-bot]

This issue has been automatically locked due to inactivity.
Please file a new issue if you are encountering a similar or related problem.

Read more about our automatic conversation locking policy.

_{This action has been performed automatically by a bot.}