Add hint for implies (using --> and not ->)

[CatarinaGamboa]

Description

Similarly to the hint given for = (use ==) we give now for -> (use -->), and refactor the code to support both.

Example

_ == true -> markSupported(this)
// produces error:
Logical implication is --> (two dashes), not ->

Related Issue

none

Type of change

• Bug fix
• New feature
• Documentation update
• Code refactoring

Checklist

• Added/updated tests under liquidjava-example/src/main/java/testSuite/ (Correct* / Error*)
• mvn test passes locally
• Updated docs/README if behavior or API changed

[rcosta358]

LGTM.