Packages project into a standalone folder at output_dir: the prebuilt runtime export
template (see find_template), renamed to the project’s name, plus a res/ folder holding
the project’s assets, scripts, and scenes — the exact layout runtime’s own res_dir/
load_manifest expect. Pure file copying, no compilation — see the export/compile
implementation plan for why.
Locates the prebuilt runtime export template next to the running editor binary: first a
templates/ subfolder (how a packaged editor release ships it), then flat next to the editor
exe (how a local cargo build — which puts every workspace binary in the same
target/<profile>/ directory — makes it available with no extra packaging step in dev).
The actual file-copying steps, factored out of export_project so they can be exercised in
a test without depending on find_template’s env::current_exe-based lookup.