Swift/Ninja: Add description to Swift object build steps

By default, Ninja displays the full build command for the object which is very verbose. Warnings are often lost in the noise, and compile errors take some searching to find. If a build step fails, Ninja will still print out the full build command, so there's no loss of useful information.

Fixes: #25853 (closed)
Cc: @etcwilde @compnerd
Topic-rename: ninja-swift-verbosity