WebpackBuilder: Remove need for react as peerDependency

[ndelangen]

What I did

I noticed that ui/components and lib/manager-api have -rightfully- a peerDependency on react.

Those packages are imported into the webpack builder causing it to also depend on react (via a peerDependency)

That causes the webpack frameworks to all depend on react (via a peerDependency).

The reason why the ui/components and lib/manager-api are used in the webpack builder is unclear:
It's likely a left-over from the olden days when the builder was used for both, and it was just always left in place in some form... never re-evaluated properly.

I left the code in place to add aliases, though I think this code should be removed.
By removing the dependencies the require.resolve used to add the alias will likely start failing in some sitations.
I wrapped it with a try-catch, so if the resolve fails, the alias is not added.

I suspect the alias might only be useful for us internally, not for outside users.

The only need you'd ever have to ensure a single version of the packages (which is what aliases are used for here) would be for addon-docs.
Addon docs should add these aliases if they are needed for some reason IMHO. Addon-docs already has a react dep, so there it would be fine.

How to test

Webpack based sandboxes should continue to work, including docs pages and MDX pages.

Checklist

• Make sure your changes are tested (stories and/or unit, integration, or end-to-end tests)
• Make sure to add/update documentation regarding your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Maintainers

• When this PR is ready for testing, make sure to add ci:normal, ci:merged or ci:daily GH label to it to run a specific set of sandboxes. The particular set of sandboxes can be found in code/lib/cli/src/sandbox-templates.ts
• Make sure this PR contains one of the labels below.

["cleanup", "BREAKING CHANGE", "feature request", "bug", "build", "documentation", "maintenance", "dependencies", "other"]

[ndelangen]

@shilman 1 of my learnings from my spike, that I deemed safe enough to extract and possible push for 7.2

I'm open to your ideas & feedback

[shilman]

HOORAY!!!! 🚀