fix(@ngtools/webpack): better AoTPlugin instance error
fix(@ngtools/webpack): better AoTPlugin instance error

Currently, having multiple @ngtools/webpack installed yields a cryptic error in typescript:

```
ERROR in ./src/main.ts
Module build failed: TypeError: Cannot read property 'newLine' of undefined
```

This happens because a plugin is found, but it isn't an instance of the right class. This makes the loader assume it's being ran without a plugin (just transpiling TS). Then it tries to load a missing tsconfig and the error above is shown.

This PR introduced better errors for both the wrong plugin instance and missing tsconfig.

```
ERROR in ./src/main.ts
Module build failed: Error: AotPlugin was detected but it was an instance of the wrong class.
This likely means you have several @ngtools/webpack packages installed.You can check this with `npm ls @ngtools/webpack`, and then remove the extra copies.
    at Object.ngcLoader (D:\work\cli\packages\@ngtools\webpack\src\loader.ts:371:19)
 @ multi ./src/main.ts
```

```
ERROR in ./src/main.ts
Module build failed: Error: @ngtools/webpack is being used as a loader but no `tsConfigPath` option norAotPlugin was detected. You must provide at least one of these.
    at Object.ngcLoader (D:\work\cli\packages\@ngtools\webpack\src\loader.ts:442:19)
 @ multi ./src/main.ts
```

See https://github.com/angular/angular-cli/issues/3781#issuecomment-272284110 and https://github.com/angular/angular-cli/issues/3781#issuecomment-311330967 for context.

maxime1992/angular-cli,DevIntent/angular-cli,Brocco/angular-cli,beeman/angular-cli,beeman/angular-cli,filipesilva/angular-cli,intellix/angular-cli,garoyeri/angular-cli,angular/angular-cli,pedroapy/angular-cli,catull/angular-cli,DevIntent/angular-cli,manekinekko/angular-cli,pedroapy/angular-cli,angular/angular-cli,Brocco/angular-cli,geofffilippi/angular-cli,escorp/angular-cli,clydin/angular-cli,vsavkin/angular-cli,RicardoVaranda/angular-cli,clydin/angular-cli,manekinekko/angular-cli,ocombe/angular-cli,nwronski/angular-cli,ocombe/angular-cli,filipesilva/angular-cli,catull/angular-cli,clydin/angular-cli,catull/angular-cli,RicardoVaranda/angular-cli,geofffilippi/angular-cli,filipesilva/angular-cli,pedroapy/angular-cli,vsavkin/angular-cli,clydin/angular-cli,hansl/angular-cli,nickroberts/angular-cli,DevIntent/angular-cli,geofffilippi/angular-cli,DevIntent/angular-cli,escorp/angular-cli,mham/angular-cli,hansl/angular-cli,nwronski/angular-cli,Brocco/angular-cli,Brocco/angular-cli,ocombe/angular-cli,mham/angular-cli,ocombe/angular-cli,geofffilippi/angular-cli,intellix/angular-cli,angular/angular-cli,RicardoVaranda/angular-cli,angular/angular-cli,maxime1992/angular-cli,maxime1992/angular-cli,ocombe/angular-cli,escorp/angular-cli,beeman/angular-cli,dzonatan/angular-cli,filipesilva/angular-cli,manekinekko/angular-cli,garoyeri/angular-cli,catull/angular-cli,Brocco/angular-cli,dzonatan/angular-cli,vsavkin/angular-cli,nwronski/angular-cli,intellix/angular-cli,hansl/angular-cli,hansl/angular-cli,DevIntent/angular-cli,dzonatan/angular-cli,nickroberts/angular-cli,garoyeri/angular-cli,mham/angular-cli,beeman/angular-cli,nickroberts/angular-cli