Make clang-format errors more helpful

[mlevesquedion]

Specifically:

• Provide a command that can be used to fix formatting problems automatically
• Make it obvious what version of clang-format to use

Also:

• Don't specify --style=google because we have a .clang-format file that already specifies that.
• Only show the version if there are formatting failures

Closes https://github.com/openxla/stablehlo/issues/2223.