fix: inherit directive and extensions in type helpers, compile unique directives

[madzhup]

This closes #1351.

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• 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?

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

What is the current behavior?

1. Directive and Extensions decorators does not inherit when using mapped types.
2. Directives metadata applying multiple times

Issue Number: #1351

What is the new behavior?

1. Directive and Extensions decorators is inherited when using mapped types.
2. Skip adding existing directive metadata

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[madzhup]

@kamilmysliwiec, can you please review this PR and merge it, if it is ok?

[kamilmysliwiec]

This looks great, thank you! It will be added in the next release.