[9.x] Fix aliasing with cursor pagination

[maximepvrt]

This fixes an issue if "as" is present in cursor pagination alias for casting a column value.

[taylorotwell]

Please describe the issue in detail. Mark as ready for review when done please. Thanks!

[maximepvrt]

Currently the getOriginalColumnNameForCursorPagination function finds the first occurrence of "as" of a dynamic column with an alias.
The correct alias is the last "as" found in a column expression.
Use explode function is bad, if multiple "as" are presents, it doesn't cut the dynamic column in 2.

I found this issue using cursorPaginate with a column dynamic expression that get the différence between two dates which I then cast to a float.