Enable passing of secure parameters

[SteveL-MSFT]

PR Summary

• Add ability to pass secureString and secureObject parameter types
• These get passed as JSON (aligned with how you'd define them in an ARM parameters file) to resources where properties match:

{
  "secureString": "string"
}

and

{
  "secureObject": { }
}

• See the test Echo resource as an example
• Enable execution of expressions for parameter default values
• Enable type validation of default values for parameters
• Removed redundant input JSON schema validation since it's already being done in the command resource method invocation

PR Context