Speed up path checking

[PaulTaykalo]

For checking if path is subpath of another, we don't actually need to use contains method.
hasPrefix will do all the job and will be faster to check.

This is because in the method, when we're checking paths, we're operating with full path's, so using contains is not only slower, but can also get false positives in some rare cases

Using this fix only, decreased project generation from about 14s to 5s on my project.

Before

After

[PaulTaykalo]

#1122 makes this PR irrelevant