I recommend `throw` over `return Promise.reject()` because:

1. It is shorter, which makes it easier to read.
2. It retains some parity between synchronous and asynchronous code. (It will continue to work as expected if those lines were extracted into a synchronous function.)

There are [some occasions](https://gist.github.com/joeytwiddle/21331531f50885345e063d59ec7f11f2) when you cannot use `throw` in place of returning a rejection, but if you are in the body of an async function then it is always safe.

The release of openapi3-ts@0.11.0 closes the gap of OAS 3.0 spec.
This PR removes most of our own type declarations for the spec.

Co-Authored-By: Raymond Feng <raymondfeng@users.noreply.github.com>

The previous script rely on `packages/build` to clean up
`loopback.io` directory after verification but it does not
install deps of `@loopback/build`.

Rework setup/build scripts to run "lerna bootstrap" as part
of "npm install".

The new setup simplifies our development workflow when changing
branches. Instead of having to remember and type multiple npm scripts,
one can run a single command:

    npm install-test # abbreviated as: npm it

Under the hood, a new "postinstall" script is calling "lerna bootstrap"
to install dependencies in individual packages.

Remove the definition of ExtensionValue from openapi-v3-types as it
is no longer used.

Remove Extendable type from openapi-spec-builder and use
ISpecificationExtension from openapi3-ts instead.

Fix openapi type guards to use a more correct `object` type instead of
`ExtensionValue`, since the guards are not dealing with any extensions.

Fix json-to-schema converter to use a different workaround
for the compiler error related to accessing index properties
on a type without any indexer.

Copies non-.ts files (json, images, text, etc.) to the outDir (dist) so file paths can remain relative. Does so for the `include` directories listed in `tsconfig.json`.

- Replace new Buffer() with Buffer.from()
- Work around nodejs/node#20278
- Upgrade to source-map-support@0.5.5

 - @loopback/authentication@0.8.1
 - @loopback/boot@0.8.1
 - @loopback/build@0.6.0
 - @loopback/cli@0.9.0
 - @loopback/context@0.8.1
 - @loopback/core@0.6.1
 - @loopback/metadata@0.6.1
 - @loopback/openapi-spec-builder@0.5.1
 - @loopback/openapi-v3-types@0.5.0
 - @loopback/openapi-v3@0.8.0
 - @loopback/repository-json-schema@0.6.1
 - @loopback/repository@0.8.1
 - @loopback/rest@0.8.0
 - @loopback/testlab@0.8.0
 - @loopback/example-hello-world@0.5.1
 - @loopback/example-log-extension@0.7.1
 - @loopback/example-rpc-server@0.5.1
 - @loopback/example-todo@0.7.1
 - @loopback/docs@0.5.1