SAI Editor: Improvements to comments involving waypoints

With https://github.com/azerothcore/Keira3/pull/2347 Waypoint-related events and actions will change to include their entry in the comments.
However, the best solution would be to add the comment related to it instead.

if NULL or '' it should use the entry value. Otherwise the comment on the first point.

For example:

On Point 2 of Path 12300 Reached -> On Point 4 of Path 'Test Creature Path' Reached

entry | pointid | position_x | position_y | position_z | point_comment
-- | -- | -- | -- | -- | --
12300 | 1 | 1 | 2 | 3 | Test Creature Path
12300 | 2 | 2 | 3 | 4 |  

Start by tracing how the SAI Editor assembles comments for waypoint-related events and actions; no file or test is named in the issue. Verify the NULL or empty-value fallback to the entry value and the first-point comment behavior using the Path 12300 example, with the displayed wording matching the requested result.

Written by the indexing model from the issue text.