Currently we save a reference to an `LView` on most DOM nodes created by Angular either by saving
the `LView` directly in the `__ngContext__` or by saving the `LContext` which has a reference to
the `LView`. This can be a problem if the DOM node is retained in memory, because the `LView` has
references to all of the child nodes of the view, as well as other internal data structures.

Previously we tried to resolve the issue by clearing the `__ngContext__` when a node is removed
(see angular#36011), but we decided not to proceeed, because it can
slow down destruction due to a megamorphic write.

These changes aim to address the issue while reducing the performance impact by assigning a unique
ID when an `LView` is created and adding it to `__ngContext__`. All active views are tracked in
a map where their unique ID is used as the key. We don't need to worry about leaks within that map,
because `LView`s are an internal data structure and we have complete control over when they are
created and destroyed.

Fixes angular#41047.