chore: bump version to 6.0.0-beta.4 w/ changelog (angular#10275)

docs(sidenav): add docs for `hasBackdrop` (angular#10287)

chore: bump version w/ changelog for 5.2.3

chore: bump 6.0.0-beta.2 w/ changelog (angular#10056)

* chore: bump 6.0.0-beta.2 w/ changelog

* add button toggle

chore: 5.2.2 w/ changelog (angular#10054)

chore: add 6.0.0-beta-0 to changelog (angular#9909)

chore: update changelog for 5.2.1 (angular#9905)

chore: bump version to 5.2.0 w/ changelog (angular#9791)

fix(keycodes): incorrect key code for nine (angular#9568)

`@angular/cdk/keycodes` package used the wrong key code for nine.

Fixes angular#9567

chore: 5.1.0 release (angular#9450)