Change NAV POSHOLD mode text to NAV LOITER on fixed wing platforms

This change comes as a result of hearing a lot of confusion from new pilots when setting up modes. Amongst the fixed wing community in general, position hold is referred to as loiter. In fact, everywhere else in inav, the settings for this mode on fixed wing are referred to as loiter too, For example, loiter direction, loiter change, and loiter radius. It makes sense to change the wording of the mode in the modes tab to loiter too. This does not effect anything as far as the navigation or functionality goes. It is a visual change only.

Fixed wing modes page example

The same FC switched to a multirotor, and fake compass added

Release notes

On fixed wing platforms. On the modes page, the navigation mode NAV POSHOLD is now displayed as NAV LOITER. The functionality has not changed. Only the name for consistency.