Format XML with prettier

[ReeceHumphreys]

After looking at a few different XML parsers, I think this integration from prettier seems to be the best.

• I looked into the Red Hat one, which is a popular VSCode extension, but there does not seem to be a way to get the formatting from it as a command line tool or in a GitHub action.
• I also looked into xmllint but its formatting wasn't that much of an improvement from what we have.
• Prettier seems to do the best job at formatting, and it's nice and easy to run from the command line. It will be integrated into the CI/CD easily. If this formatting is okay, I will update this PR to update the actions.

[bernardnormier]

It would be good to open the projects with Visual Studio (not VS code) to make sure VS does not immediately reformat all the project files.

[ReeceHumphreys]

@bernardnormier Just opened the IceRpc.sln on my mac with visual studio and nothing changed! I have 0 familiarity with Visual Studio so im not sure if this is sufficient to show that the formatting is preserved. @pepone could you verify if Visual Studio leaves the files with the new formatting?

[pepone]

could you verify if Visual Studio leaves the files with the new formatting?

Yes, formatting remains the same after opening the solution in Visual Studio 2022 on Windows.