New feature suggestion: Allow specifying a function to transform the value of the filter tooltip

[yamadayutaka]

If the value displayed in a cell is different from the internal value, the value in the filter tooltip will be different than expected.

For example, if a value of type Date is displayed as follows.

I would like to be able to specify a function to transform the value of the filter tooltip.

I have already implemented it and would like to create a PR.