feat: do not use rxjs >= 7 exclusive feature to not break backward co…

…mpatibility (#1520)

PR Checklist

Please check if your PR fulfills the following requirements:

[ ] The commit message follows our guidelines: https://github.com/ngxs/store/blob/master/CONTRIBUTING.md#commit
[ ] Tests for the changes have been added (for bug fixes / features)
[ ] Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

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

What is the current behavior?

Issue Number: N/A

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[ ] No

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (d6dc030) 82.27% compared to head (b037315) 82.28%. Report is 3 commits behind head on master.

Files	Patch %	Lines
...te/src/date-suggestion/tokens/first-day-of-week.ts	90.90%	1 Missing :warning:
...ectives/src/convert-case/convert-case.directive.ts	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1521 +/- ## ========================================== + Coverage 82.27% 82.28% +0.01% ========================================== Files 618 619 +1 Lines 8836 8847 +11 Branches 1710 1711 +1 ========================================== + Hits 7270 7280 +10 - Misses 1484 1485 +1 Partials 82 82 ``` | [Flag](https://app.codecov.io/gh/Angular-RU/angular-ru-sdk/pull/1521/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Angular-RU) | Coverage Δ | | |---|---|---| | [cdk](https://app.codecov.io/gh/Angular-RU/angular-ru-sdk/pull/1521/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Angular-RU) | `79.75% <92.00%> (+0.01%)` | :arrow_up: | | [jest](https://app.codecov.io/gh/Angular-RU/angular-ru-sdk/pull/1521/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Angular-RU) | `80.83% <ø> (ø)` | | | [ngxs](https://app.codecov.io/gh/Angular-RU/angular-ru-sdk/pull/1521/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Angular-RU) | `96.34% <ø> (ø)` | | | [summary](https://app.codecov.io/gh/Angular-RU/angular-ru-sdk/pull/1521/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Angular-RU) | `82.28% <92.00%> (+0.01%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Angular-RU#carryforward-flags-in-the-pull-request-comment) to find out more.

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

Angular-RU / angular-ru-sdk