Various tweaks for omp-stdlib

[NexiusTailer]

Tweaks for OPEN_MP_TAGS

This is going to fix 2 possible mistakes:

1. Having extra tag LANDING_GEAR_STATE among all other SA-MP tags, and looks like there's no reason for it to be there.
2. Having 9 tags in a list of OPEN_MP_TAGS on the old compiler variant instead of 8 ones. Considering that it can have no more than 16 tags in such lists (8 tags in CUSTOM_TAG_TYPES + 8 tags listed in the #define OPEN_MP_TAGS)

Tweaks for return value tags

This is going to fix 3 cases where a bool: tag was added for natives which should return string length (integer value) instead of success/failure (true/false):

1. GetWeaponName
2. GetSVarNameAtIndex
3. GetPVarNameAtIndex

Also related to open.mp #1098

[NexiusTailer]

Updated, now there are only changes which I consider important.
As fas as I tested all this, no issues were found by the last couple of weeks.