[#881] Handle implicit default entrypoint in mkEntrypointsMap

Description

Problem: There is an ambiguity about mkEntrypointsMap function - if there is no explicit default entrypoint, will it contain default pointing to root or not?

Solution: Make the choice explicit via an additional parameter. This has a knock-on effect on entrypoint coverage testing facilities in Cleveland: if before they always ignored the implicit default, now they check the implicit default in the contract if it is explicitly expected. This seemed like the most useful behaviour that doesn't break compatibility too much.

Related issue(s)

Resolves #881 (closed)

✅ Checklist for your Merge Request

Related changes (conditional)

• Tests (see short guidelines)

  • If I added new functionality, I added tests covering it.
  • If I fixed a bug, I added a regression test to prevent the bug from silently reappearing again.

• Documentation

  • I checked whether I should update the docs and did so if necessary:
    • Root README and other README.md files
    • Haddock
    • docs/
  • I updated changelog files of all affected packages released to Hackage if my changes are externally visible.

Stylistic guide (mandatory)

• My commits comply with the following policy.
• My code complies with the style guide.