fix(component-store): adjust updater to accept partials

[alex-okrushko]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/ngrx/platform/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Documentation has been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

Adjust updater typings.
New type would work properly with Partial<Obj> interfaces, as well as with simple unknown if that's what the developer wants to pass to the updater.
It would still return () => void if the second argument is not specified.

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Other... Please describe:

Closes #2754

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[alex-okrushko]

Ran into the issue with enums when syncing it into google3. (added WIP for now)

[alex-okrushko]

Also ran into this case cartant/ts-snippet#37

[ngrxbot]

Preview docs changes for 22de7f7 at https://previews.ngrx.io/pr2765-22de7f7f/