Add support for adding build tool plugins to targets (#1374)

* Add support for adding build tool plugins to targets

* Added Plugin validation

* Added some tests

* Limited the minimum version to 5.7 Swift

* Update .gitignore

Co-authored-by: freddi(Yuki Aki) <freddi-kit@users.noreply.github.com>

* Update CHANGELOG.md

Co-authored-by: freddi(Yuki Aki) <freddi-kit@users.noreply.github.com>

* Update CHANGELOG.md

Co-authored-by: freddi(Yuki Aki) <freddi-kit@users.noreply.github.com>

* Update Docs/ProjectSpec.md

Co-authored-by: freddi(Yuki Aki) <freddi-kit@users.noreply.github.com>

* Added a fixture for testing plugins

* Update CHANGELOG.md

* Installed the release version of XcodeProj

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Co-authored-by: freddi(Yuki Aki) <freddi-kit@users.noreply.github.com>