* test(defer): add failing dtslint test

* fix(defer): use overload sig for void factory

Closes #4804

* docs: added Synchronous Assertion section.

Added Synchronous Assertion section to make the use of flush() clearer.
Change scheduler variable name to match initialisation example.

* docs: fixed link to Synchronous Assertion

* docs: changed Synchronous Assertion example test

PR review requested improved example

* docs: simplified Synchronous Assertion example

Clarify that refCount is an operator and not a method used directly on a ConnectableObservable.

Closes #4664

* test(defer): add failing dtslint test

* fix(defer): restrict allowed factory types

* test(defer): add a sometimes-returns dtslint test

* test(Subscription): Update subscription tests

* Cleaned up wording
* Moved positive cases to the top
* Grouped unsubscribe() tests together

* Fix the linter

* test(dtslint): add dtslint test for merge operator (#4093)

* test(dtslint): change dtslint test for merge operator to use helpers (#4093)

* test(dtslint): add zipAll

* update tests slightly

* test(dtslint): add more type checks

* test(dtslint): fixup add more type checks

* test(dtslint): fix lint problems

)

* test(dtslint): add dtslint test for of observable static function (#4093)

* test(dtslint): change of observable static function dtslint test to use helper (#4093)

See also section extended with all related operators.

This closes #4922

)

* test: add test for side-effects

* refactor: remove toplevel property access

* docs(operator): add missing marble diagramms

* Revert "docs(operator): add marbel diagramm to distinctUntilChanged"

This reverts commit 6bf3aae.

* Revert "docs(operator): add fitting description and diagramm to distinctUntilKeyChanged"

This reverts commit 98c23b5.

* Revert "docs(operator): add missing marble diagramms"

This reverts commit b61acad.

* docs(angular): update angular/ codelyzer/ typescript version

* docs(angular): fix minor errors after migration

* chore(eslint): update version

* docs(app): upgrade to angular 8

* docs(migration): fix wrong polyfill imports