add detect sharp corners

[kabirkedia]

Summary of Changes

Adds the function detect_sharp_corners to detect sharp corners as addressed in issue #1708

Release Management

• Affected package(s): PMP
• Issue(s) solved (if any): fix Improvements for PMP::isotropic_remeshing #1708
• Feature/Small Feature (if any): add detect_sharp_corners function
• License and copyright ownership:

[janetournois]

Now vertices incident to 1 or more than 2 sharp edges are set to be "sharp".
There are two more cases to handle :

1. vertices incident to exactly 2 sharp edges that form a sharp angle together
2. vertices incident to no sharp edges and that form a sharp angle (like the tip of a cone)

This PR is very related to #4084 that includes experimental code for features detection

[sloriot]

@janetournois still targeting 5.4?

[lrineau]

@janetournois still targeting 5.4?

Jane, do we still want it for next release? The code freeze is... supposed to be today.

[janetournois]

Sorry I had missed the previous message.
There is no small feature yet so let's postpone it to 5.5, and make it complete by then