refactor: readonly struct properties and hide internals

[eladb]

This change upgrades the repo to jsii 0.8.0 which requires that all struct types (data interfaces like our "Props" interfaces) will be marked readonly in order to ensure they can be passed by-value.

The new jsii version also hides all members marked as @internal which means that those APIs will not be available from outside the framework.

Fixes awslabs/cdk-ops#321

BREAKING CHANGE: stack._toCloudFormation method is now unavailable and is replaced by @aws-cdk/assert.SynthUtils.toCloudFormation(stack).

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Pull Request Checklist

• Testing
  • Unit test added (prefer not to modify an existing test, otherwise, it's probably a breaking change)
  • CLI change?: coordinate update of integration tests with team
  • cdk-init template change?: coordinated update of integration tests with team
• Docs
  • jsdocs: All public APIs documented
  • README: README and/or documentation topic updated
• Title and Description
  • Change type: title prefixed with fix, feat will appear in changelog
  • Title: use lower-case and doesn't end with a period
  • Breaking?: last paragraph: "BREAKING CHANGE: <describe what changed + link for details>"
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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license.

[hoegertn]

What is the new/correct way to modify Props after creating the object?

I use this currently to set fields conditionally after creating the object with my shared config:
e.g. https://github.com/taimos/cdk-constructs/blob/master/lib/alexa/skill.ts#L57

[eladb]

@hoegertn not sure what this line points at :-)

[hoegertn]

Sorry, I changed it already. Here is the link to the revision: https://github.com/taimos/cdk-constructs/blob/e2279f2bcc004374dcbba5c14be61dd78ab30158/lib/alexa/skill.ts#L56

I changed it in master, but I am not really happy with the code.

[yueyingcui]

@eladb since the attributes are readonly now, could you share a recommended way to modify/dynamically create Props objects?

[eladb]

See #2372

[yueyingcui]

Thanks!

[mergify]

Thanks so much for taking the time to contribute to the AWS CDK ❤️

We will shortly assign someone to review this pull request and help get it
merged. In the meantime, please take a minute to make sure you follow this
checklist:

• PR title type(scope): text
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