SILDebugScopes: Don't ignore ConditionalClauseInitializerScope.
ConditionalClauseInitializerScope often create redundant scopes, however, they
are needed to correctly represent the scopes in an expression such as:
if case .something(let foo), let foo = foo.
This patch changes SILGen to lower them 1:1 from ASTScopes.
rdar://110841130
