Instantiate classes per scenario

[gaeljw]

This aims to fix #1

Content:

• added tests to highlight the "isolation" issue bringed by loading glue classes once for all scenarios
• fix this behavior in a similar way to how the Java8/Lambda implementation does
• documentation for future developers

Breaking changes introduced:

• this is an internal breaking change, users should not be affected unless users have scenarios relying on a state shared between multiple scenarios using glue classes

Tests:

• Added some as part of the PR
• Currently using this SNAPSHOT version on a private codebase with hundreds of features to ensure non regression

[gaeljw]

I confirm I didn't had any issue (except the ones from Cucumber 5 upgrade itself with some null values in datatables) on the codebase against which I ran the test.
I wouldn't say we use all the features offered by Cucumber in this codebase but pretty confident for the main ones.