build: serve ivy dev-app with lazy loading

[devversion]

• Updates the Ivy script/build pipeline to support lazy-loading with the dev-app.
• Removes duplicate lazy routes (otherwise causes error within rollup; to be in sync: build: remove duplicate route definitions #15558)
• Ensures Ivy Angular install script ensures clean Ivy packages are installed
• Ensures Ivy build.sh script works if Gulp is not installed globally.

[ngbot]

I see that you just added the pr: merge ready label, but the following checks are still failing:
     status "ci/circleci: api_golden_checks" is failing
     status "ci/circleci: build_release_packages" is failing
     status "ci/circleci: lint" is failing
     status "ci/circleci: prerender_build" is failing
     status "ci/circleci: tests_browserstack" is failing
     status "ci/circleci: tests_local_browsers" is failing
     status "ci/circleci: tests_saucelabs" is failing
     missing required labels: target: *

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[crisbeto]

One thing that can up in the last Ivy meeting that might be nice: currently when you build, you end up with some untracked files under src. Can we add those to the gitignore? For reference:

[devversion]

@crisbeto Looking into that in a separate PR. @kara mentioned it as well but I didn't notice such files last time. will double-check.

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