Add Assert assertions to Pester

[nohwnd]

Fix #1423

PR Summary

This PR adds assertions from Assert module to Pester, to serve as a base for future assertions and to live side-by-side with the existing Should assertions that are based on parameter sets.

PR Checklist

• [x] PR has meaningful title
• [x] Summary describes changes
• [ ] PR is ready to be merged
  • If not, use the arrow next to Create Pull Request to mark it as a draft. PR can be marked Ready for review when it's ready.
• [x] Tests are added/update (if required)
• [ ] Documentation is updated/added (if required)

[fflaten]

We should probably decide on #2381 soon, so these assertions can either implement it - or not. 🙂

[nohwnd]

/azp run

[azure-pipelines[bot]]

Azure Pipelines could not run because the pipeline triggers exclude this branch/path.

[nohwnd]

This PR is getting too much, will start refactoring the existing assertions towards common pattern (to make them more similar to the current Should -* assertions), instead of adding new ones.

• [x] rename all files to Should-*
• [x] rename all test files to should-*, and use Should-Assertions in the tests instead of Assert- to make sure we export them. Get rid of inpestermodulescope
• [x] review messages so they look similar to existing assertions
• [x] write help
• [x] make type specific assertions require that type (e.g. should-*string needs string input)
• [ ] Fix assertion for collections - will do later
• [x] Make sure that assertions throw for no input?

[nohwnd]

Should be good enough to release in 6.0.0-alpha1 so we can get other people to look at this. Please give at another quick review @fflaten .

[fflaten]

With 7k linediff I can't promise "quick", but I'll try tomorrow when my browser is done rendering the diff. 🙂 I'll trust your tests for functionality.

[nohwnd]

I've fixed all the suggestions, and what I did not fix I moved to issues :) Pls approve.