fix(@ngtools/webpack): `getCurrentDirectory` should not return a devkit path
fix(@ngtools/webpack): `getCurrentDirectory` should not return a devkit path

At the moment we are leaking devkit paths as `getCurrentDirectory` is used by the ngtsc compiler if no `rootDir` directories is provided.

`getCurrentDirectory` is also used to contruct the `rootDirs` option which is causing this to be incorrect as under Windows as `rootDirs` will be have an invalid value example: `/c/foo/bar`

This PR complements https://github.com/angular/angular/pull/29151

**Note** that this currently works because we are normalizing paths with posix seperators and is mimicking the behaviour of the logical file system used by the ngtsc.

Fixes: #13849

geofffilippi/angular-cli,Brocco/angular-cli,ocombe/angular-cli,Brocco/angular-cli,DevIntent/angular-cli,catull/angular-cli,Brocco/angular-cli,beeman/angular-cli,manekinekko/angular-cli,hansl/angular-cli,filipesilva/angular-cli,Brocco/angular-cli,clydin/angular-cli,manekinekko/angular-cli,Brocco/angular-cli,clydin/angular-cli,catull/angular-cli,filipesilva/angular-cli,geofffilippi/angular-cli,hansl/angular-cli,beeman/angular-cli,DevIntent/angular-cli,filipesilva/angular-cli,ocombe/angular-cli,ocombe/angular-cli,angular/angular-cli,angular/angular-cli,ocombe/angular-cli,hansl/angular-cli,catull/angular-cli,clydin/angular-cli,clydin/angular-cli,hansl/angular-cli,beeman/angular-cli,beeman/angular-cli,angular/angular-cli,DevIntent/angular-cli,ocombe/angular-cli,filipesilva/angular-cli,manekinekko/angular-cli,geofffilippi/angular-cli,catull/angular-cli,geofffilippi/angular-cli,DevIntent/angular-cli,DevIntent/angular-cli,angular/angular-cli