The dashboard's source-routed runner ships idedata.json with bare
basenames in prog_path and extra.flash_images[*].path (the receiver's
build-host absolute paths don't resolve on the offloader, and the
in-memory Web Serial consumer keys by basename). Without this change,
the dashboard would have to write a fresh idedata.json into the staging
tmpdir on every install just to flip basenames to absolute paths.
Resolve relative paths in the prebuilt idedata against CORE.prebuilt_dir
so both the dashboard's wire format and a hand-built directory with
absolute paths work. cc_path is left alone because it points at a
PlatformIO toolchain binary outside the prebuilt dir; the offloader's
own PIO install provides the matching binary.
Issue: esphome/device-builder#570
Issue: esphome/device-builder#572
J. Nick Koston
f4607cb521