Scaladoc: member filter should not be case-sensitive

## Scaladoc version

Nightly (6.02.2022) https://dotty.epfl.ch/api/index.html

## Expectation

Member filter should not be case-sensitive.

## Example

![Peek 2022-02-06 17-17](https://user-images.githubusercontent.com/39772805/152690355-89f98687-b337-4d1f-a7aa-01d75269a273.gif)
