Deprecate before observers

Also remove usages of public `addBeforeObserver` in ember internals.
[BUGFIX] Allow Ember.Select to have selection from a Promise
when multiple=false
Replace listenersDiff and listenersUnion with a single function accumulateListeners; rename parameter
remove ember-data hooks for making things sync

When they should instead be scheduled within
the ember run loop

refs emberjs/data#2477
Extract `appendView`, `destroyView` for testing

Defining `appendView` and `destroyView` in multiple tests is verbose,
repetitious, and copy-paste-error prone.
[DOC beta] An attempt to update the Ember.run.bind docs per #9735
Merge pull request #9769 from seanpdoyle/view-helpers-extraction

Extract `appendView`, `destroyView` for testing
Merge pull request #9764 from fivetanley/remove-ember-data-cruft

remove ember-data hooks for making things sync
Update to htmlbars@0.2.0
Merge pull request #9765 from mmun/template-objects

Update to htmlbars@0.2.0
Merge pull request #9646 from BookingSync/select-promises

[BUGFIX] Allow Ember.Select to have selection from a Promise
Update to HTMLBars 0.3.0.

Fixes AST walker to be compatible with latest HTMLBars version (which
updated to latest Handlebars AST).
Merge pull request #9772 from rwjblue/htmlbars-ast-walker-update

Update to HTMLBars 0.3.0.
Failing tests for href, class, booleans, value
Introduce AttrNode, new HTMLBars attribute syntax
Port attrs and classes via bind-attr to AttrNode
Add SVG attribute support
Support maxlength and nonmatching reflections
Add a feature flag for attribute syntax
Remove some closures