Feat code actions forall calc

[MikaelMayer]

What was changed?

First, for implicit assertions, if they are surrounded by a declaration that supports by clause (like AssertStmt or CallStmt), the by clause is preferred to inserting the assertion before.

And that works also for well-formedness, since well-formedness is now proved by by-blocks (thanks @keyboardDrummer for that, and @alex-chew for creating Dafny expressions for well-formedness)

Moreover, if a by clause already exist, the code action will insert into it.

Second, assertion of foralls now support a proof sketch by inserting forall statement

Third, assertions of equalities or equivalence now support a proof sketch by inserting a calc statement.

The code for inserting such proof sketches has been refactored so that it will be even more easy to extend in the future.

How has this been tested?

• Tests were updated for the insertion point (var....by) when possible and insert there if it already exist.
• Tests were added for foralls, equalities and equivalences, and also new insertion points

By submitting this pull request, I confirm that my contribution is made under the terms of the MIT license.