implement eager_grouping for expression clauselists

implement eager_grouping for expression clauselists

the expression clauselist feature added in #7744 failed to accommodate
this parameter that is used only by the PostgreSQL JSON
operators.

Fixed 2.0 regression caused by :ticket:`7744` where chains of expressions
involving PostgreSQL JSON operators combined with other operators such as
string concatenation would lose correct parenthesization, due to an
implementation detail specific to the PostgreSQL dialect.

Fixes: #10479
Change-Id: Ic168bf6afd8bf1cfa648f2bad22fdd7254feaa34