Improved parameter names for call signatures resulting from unions

[dragomirtitian]

Fixes #31845

[fatcerberus]

calledUnionsOfDissimilarTyeshaveGoodDisplay.ts

I chuckled a bit at this filename, not sure why.

[dragomirtitian]

@fatcerberus It was there when I started, it amused me too 😄

[dragomirtitian]

@weswigham Any thought on this PR since it touches your code ? The issue was that if the methods had different parameter length combineUnionParameters would end up calling getParameterNameAtPosition with an invalid parameter index. getParameterNameAtPosition would just return the string 'unknown' in this case and since this was different from the name in the longer function it would fall back to `arg${i}`.

The fix was to use the name of the parameter in the function with more parameters.

[weswigham]

Seems like an improvement to me ❤️