Fix rational to decimal on type_cast_from_user
Change class evaluation for Rationals in cast_value
Fix case statement to use ::Numeric and ::String
Fix decimal_test module and add new test for object responding to to_d
Merge pull request #16188 from marianovalles/fix_rational_to_decimal_type_cast

Fix rational to decimal on type_cast_from_user
Prefer if/else for this case

One of the branches is using a proc to check if the value respond_to a
method so it is better to not do case comparations
Disable some tests on SQLite

These tests were passing before because the precision were not using to
cast the value. Not it is being used so it would fail on sqlite3