feat: Upgrade to Angular 12 and include partial Ivy compilation support

PR Checklist

Please check if your PR fulfills the following requirements:

[x] The commit message follows our guidelines: https://github.com/ngneat/forms-manager/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
[x] 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:

What is the current behavior?

Angular 12 is not supported, and package is compiled with View Engine.

Issue Number: #60

What is the new behavior?

Package now supports Angular 12 and is compiled with partial Ivy support.

Does this PR introduce a breaking change?

[x] Yes
[ ] No

Other information

Attempted to follow migration path similar to other packages. There are possibly some devDependencies that may no longer be necessary, however I've attempted to update them as best I can to ensure compatibility in Angular 12.

ngneat / forms-manager

feat: Upgrade to Angular 12 and include partial Ivy compilation support #61