Analyzer Ideas: use non-whitespace, unique DisplayNames on DataRows

## Summary

while copy and pasting, one might forget to change the DisplayName of a DataRow.
There is a Analyzer already for detecting duplicate DataRow data itself. this should be "extended" to DisplayNames

## Background and Motivation

writing some Tests for Whitespace-Adjustment, using the DisplayName sets a non-whitespace name to the DataRows.
a)

b)

## Proposed Feature

a) detect duplicate DisplayNames on DataRows
b) perhaps in the DisplayName detect whitespace, but especially line breaks, since it can lead to confusing Output in `dotnet test` or Visual Studio Test Explorer for TestCase Name (maybe even configurable, if i.e. single space are allowed?)
- also consider DataRows string-arguments, which contain spaces/line breaks without a ("clean") DisplayName

DataRows with non-strings, or strings without whitespace should still be allowed as-is, obviously. This is to combat confusing/whitespace Names in test output etc.

This will probably flag a lot of our own tests, but i'd rather have to deal with that by an analyzer rather than by a broken CI build.

## Alternative Designs
(only custom/private analyzer)

Start by locating the existing analyzer that detects duplicate DataRow data and trace its tests and diagnostics. Define how it should handle duplicate or whitespace-containing DisplayNames and string arguments, then add coverage showing valid non-string and non-whitespace cases remain accepted.

Written by the indexing model from the issue text.