meson install now supports user-preferred root elevation tools

Previously, when installing a project, if any files could not be installed due to insufficient permissions the install process was automatically re-run using polkit. Now it prompts to ask whether that is desirable, and checks for CLI-based tools such as sudo or opendoas or $MESON_ROOT_CMD, first.

Meson will no longer attempt privilege elevation at all, when not running interactively.