Improve map test coverage

[abendt]

Context

See issue #2894

Changes

• add more tests for map to improve test coverage
  i have ported some of the tests from here: https://github.com/arrow-kt/arrow-core/tree/master/arrow-core-test/src/main/kotlin/arrow/core/test/laws
• ensure that the generated maps used in the test share enough keys
  otherwise not all code paths are executed. i have added a test and left some comments that ensures that the generated maps share enough keys. With the previous solution often maps didn't share any keys. I was also thinking about to implement a specialized Arb for this task (see discussion here property testing: generate two maps that share some keys kotest/kotest#3459)

Edit: with awesome help from the kotest slack i implemented a specialized Arb (see the linked issue)

[serras]

Nice work! I've left a small comment, because I think that associate reads better than map + toMap most of the times.

[serras]

@abendt I've decided to remove the tests that checked that map2 and map3 where correct, because they introduce some flakiness in the tests (you may always get a bad run in which the property isn't satisfied).