Fix sample warnings and add samples to upm metadata

[johanhelsing]

Pull request checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
• No compiler errors or warnings

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

Issue Number

Issue Number: #50

Previous attempt: modesttree#220

What is the current behavior?

Adding extenject or triggering re-import produces 54 warnings. Sample games do not show up in package manager.

What is the new behavior?

No warnings because of sample files being outside asmdefs remain.

Samples show up in the inspector

Does this introduce a breaking change?

• Yes
• No

Other information

On which Unity version has this been tested?

• 2021.3 LTS
• 2020.3 LTS
• 2020.2
• 2020.1
• 2019.4 LTS
• 2019.3
• 2019.2
• 2019.1
• 2018.4 LTS

Scripting backend:

• Mono
• IL2CPP

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[Mathijs-Bakker]

Merged.
Thank you Johan!

[Mathijs-Bakker]

Closes #50 #51