Replace entire dep sets, so peer loops don't lock

[isaacs]

Discovered an interesting issue with the following dependency set:

{
  "devDependencies": {
    "webpack-dev-server": "^3.11.0",
    "@pmmmwh/react-refresh-webpack-plugin": "^0.4.3"
  }
}

webpack-dev-server here has a peerDependency on webpack v4. But, the
dependencies of @pmmmwh/react-refresh-webpack-plugin have peer
dependencies on webpack at 4 || 5.

So, a resolution should be possible. Since the
@pmmmwh/react-refresh-webpack-plugin package is alphabetically first,
it loads its deps, and ends up placing webpack@5 to satisfy the dep with
the latest and greatest. Then when webpack-dev-server gets to its
eventual peer dep on webpack, it can't replace it, because webpack@5
has a dependency on terser-webpack-plugin@^5.0.3, which in turn has a
peer dependency on webpack@5.4.0.

When we check to see if webpack 5 can be replaced, we find it has a
dependent, and reject the replacement. But that dependent is only
present as a dependency of the thing being replaced, so should not be
considered.

Second, while the source of the terser-webpack-plugin is webpack, it
cannot be installed there, because it has peer deps that are also peer
deps of webpack. So, we must place it in the root node_modules, but
were not attempting the "source" location overrides, because the root is
not the source. This was a second issue resulting in ERESOLVE errors
even when --force was applied, with the following dependency set:

{
  "devDependencies": {
    "webpack-dev-server": "^3.11.0",
    "webpack": "^5.0.0"
  }
}

Fixes: #180
Fixes: npm/cli#2123

[nlf]

👍 looks good, this makes sense!