Implement nicer property DSL for Job DSL and Pipeline

[timja]

relates to jenkinsci/matrix-auth-plugin#144
Fixes #467

---

Job DSL:

folder('generated') {
  properties {
    azureAdAuthorizationMatrix {
      inheritanceStrategy {
          nonInheriting()
      }
      entries {
        group {
          name('A group (7fe913e8-6c9f-40f8-913e-7178b7768cc5)')
          permissions([
            'Job/Build',
            'Job/Configure',
            'Job/Read'
          ])}
        user {
          name('c411116f-cfa6-472c-8ccf-d0cb6053c9aa')
          permissions(['Job/Delete'])
        }
      }
    }
  }
}

The corresponding Pipeline snippet looks like this, according to Snippet generator (formatted for readability):

properties([
  azureAdAuthorizationMatrix([
    user(name: 'c411116f-cfa6-472c-8ccf-d0cb6053c9aa', permissions: ['Job/Delete']),
    group(name: 'A group (7fe913e8-6c9f-40f8-913e-7178b7768cc5)', permissions: [
      'Job/Build',
      'Job/Configure',
      'Job/Read'
    ])
  ])
])

Testing done

Manually checked all the above looks correct in the UI, haven't actually tried with any of the users.
I fixed the pipeline syntax page which wasn't working before.

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