pressure-vessel: Update Flatpak-derived code to Flatpak 1.14.6

• flatpak_bwrap_free: Realign with the version in flatpak 1.15.x

  No functional change, but the order in which things were freed is slightly different in the version I upstreamed to Flatpak.

• pressure-vessel: Update Flatpak-derived code to Flatpak 1.14.6

  Many of the changes are #if 0. Main changes that have a practical effect on steam-runtime-tools:

  • flatpak_exports_add_path_expose(), etc. return a GError, which we convert into a warning- or info-level message in the same way that flatpak_context_export() would. To facilitate this, add helper functions in pressure-vessel/exports.c.

  • flatpak-context.c is no longer included here, and all of the declarations in its header are now #if 0. The only parts that we use are the enums in the header, which are still present; the array dont_mount_in_root, which has been moved into wrap-setup.c; and the new log_cannot_export_error function, which has been moved into exports.c.