feat(angular): add support for custom elements build

[willmartian]

Pull request checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
• Build (npm run build) was run locally and any changes were pushed
• Lint (npm run lint) has passed locally and any fixes were made for failures

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

Issue Number: N/A

What is the new behavior?

Does this introduce a breaking change?

• Yes
• No

Other information

Prereqs:

• Release Angular output target: feat(angular): add support for custom elements build stenciljs/output-targets#200
• feat(angular): build for angular 12.0 #23970 to make use of import type https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-8.html#type-only-imports-and-export

[willmartian]

Blocked on lazy loading Ionicons SVGs while using the CE build. Closing until this is addressed.

[GeorgeDigital]

Hi. Any News for custom element builds in angular? Would be very nice if this works also in angular.