Power Display: Allow custom VCP Input Source values

### Description of the new feature / enhancement

Currently, in Power Display, we can only switch among Input Sources defined in Detected VCP codes. Many monitors have a difference set of reported input sources than its actual input sources.

For example, my monitor reports

```
Detected VCP Codes:
--------------------------------------------------

Input Source (0x60)
Values: VGA-1 (0x01), DVI-1 (0x03)
```

But its actual Input Source (0x60) capabilities are: HDMI-1 (0x05), HDMI-2 (0x06) and DisplayPort (0x0F). I cannot switch to any of these using Power Display.

Please allow custom VCP (Virtual Control Panel) Input Source Codes.

### Scenario when this would be used?

Switching between Input Sources for an external monitor supporting DDC/CI.

### Supporting information

This is true even after I set custom name mappings, which is only overriding the default names already in the reported value list, but not adding new values to the Input Source list.

No files or tests are named. Start by locating Power Display's input source handling and the custom name mapping flow, then trace how reported VCP values populate the selectable list. Done means custom VCP input source codes such as HDMI-1, HDMI-2, and DisplayPort can be selected for a DDC/CI monitor.

Written by the indexing model from the issue text.