Lack of quoting causes issues when files have spaces or are empty names.
Additionally, some arrays (though single elements) were treated like
simple variables.

The careful reader will note that I have left BUILD_ARGS

dotnet build "${ROOT_PATH}"/CrossPlatform.sln ${BUILD_ARGS}

untouched, because it contains spaces meant to separate arguments. Word
expansion is somewhat desired there (I believe) to ensure the arguments
are properly parsed. Unfortunately, BUILD_ARGS may contains paths with
spaces in them, causing this to still fail.

Fix #22259