Pass columnkey to filterFunction method for custom filter

[moet78]

When trying to generate the column definition with script, to handle mutable column returned from backend, I also need to handle different custom filter function on some of the columns.

However, currently the getFilteredContent in fixtable-grid.js only pass 'row' and 'filterValue' into the filterFunction, meaning there is no easy way to identify which column I am working on, making it difficult to construct the column definition with script.

Can we also pass the columnkey into the filterFunction? That would make constructing a fixtable with dynamic column list easier, with minimum change to the code.