fix(pluginHandlers): properly check if path is inside another

[raphinesse]

Motivation and Context

The current check for "Is path A inside path B?" relies solely on prefix checking. In general, that is not robust enough.

A real-world example where it fails, is when Api.createPlatform is called with a destination that is outside of process.cwd(). For example a temp dir during a test. This occurred when refactoring E2E tests.

This relies on proper test cleanup as implemented in #1013.

Description

Use is-path-inside library.

Testing

• Api.createPlatform now works as expected
• added regression test
  The new test calls copyFile with the same arguments as Test#006 and Test#007 with the sole difference that the project dir is relative to the current dir.