DraftV3ItemsSyntaxChecker: no need to clear info on entering validation

Calling the validator will yield other messages.

Signed-off-by: Francis Galiegue <fgaliegue@gmail.com>
Add recursive syntax validation for dependencies (draft v3)

Signed-off-by: Francis Galiegue <fgaliegue@gmail.com>
Add recursive syntax validation for extends

Signed-off-by: Francis Galiegue <fgaliegue@gmail.com>