proprietary licenses: report copyright holder/vendor

### Description

Some license rules for proprietary licenses are specific to a single vendor, yet scancode does not report the copyright holder. An example is `proprietary-license_663.RULE` which is specific to MediaTek. It would be useful to report the vendor.

### System configuration

```
$ ./scancode --version
ScanCode version: v32.0.0rc3-105-g6b1c2ce1d4
ScanCode Output Format version: 3.0.0
SPDX License list version: 3.20

```