fix: use custom formatter when filtering rows

As datatable renders only some rows at a time and sets each cell's html property based on that rendering, so when someone filters things and only looks at some rows without scrolling the whole grid and tries to filter things (when there is a custom cell formatter), they won't be able to see the data as the filtering is done based on cell's content not html (as it's not set at that point)

For example datatable renders date by default in the format: yyyy-mm-dd but if someone uses a custom formatter and changes it to say dd-mm-yyyy, they won't be able to filter/see the data properly

before:

https://user-images.githubusercontent.com/32034600/173000480-afd08e9b-67d0-40e0-9a2f-89f8c4a2b3f1.mov

after:

https://user-images.githubusercontent.com/32034600/173000453-b34728b5-7019-4cab-8192-37e7f1e2ce93.mov

frappe / datatable

fix: use custom formatter when filtering rows #158