Fixed CORE-4118: Expression index may be not used for derived fields or view fields. Also, generalized the old trick with CAST in expression indices.

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/branches/B2_5_Release@58272 65644016-39b1-43b1-bf79-96bc8fe82c15