Bug 421328 - Performance issue with TraitUtils.parse()

The AST visitor used in TraitUtils.parse() is optimized for performance
to traverse only the nodes where use statements can be legally found and
not go deeper in the AST tree.

Tests added to the suite.

Bug: 421328
Change-Id: I5902222bce4b3b7f31eb2dd9862a7e6d20e75fb3
Signed-off-by: Kaloyan Raev <kaloyan.r@zend.com>