refactor(angular, react, vue): add missing test app msg

[thetaPC]

Issue number: N/A

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What is the current behavior?

The packages, Angular, React, and Vue, will accept any app_dir parameter when passing it to the build script. This can lead to a user to entering a directory that doesn't exist within test/apps. If this happens, then the build folder will include an incomplete test app.

For example:

1. ./build ng13
2. This creates a build/ng13 folder, but the folder only contains the contents from the base folder. This causes it to be incomplete.

What is the new behavior?

• Provides a message that the provided app directory doesn't exist.
• Does not create the incomplete app when an invalid app directory is given.

Does this introduce a breaking change?

• Yes
• No

Other information

N/A

[averyjohnston]

Tested locally and works great, thank you!