MGLMultiPoint (MGLPolyline, MGLPolygon) should allow removing coordinates

[1ec5]

Now that #6565 has landed, it’s possible to replace a segment (series of coordinates) of an MGLMultiPoint, MGLPolyline, or MGLPolygon with a segment of equal length, append coordinates to the end of the shape, or replace a segment at the end while appending. However, it isn’t possible to truncate (shrink) the shape, splice out (delete) a segment in the beginning or middle of the shape, or replace all the coordinates without replacing the shape annotation outright (since we try to avoid memcpy() of overlapping memory).

To complete the feature we added in #6565, we need to add the following methods to MGLMultiPoint:

• -setCoordinates:count:
• -replaceCoordinatesInRange:withCoordinates:count: (and remove or deprecate -replaceCoordinatesInRange:withCoordinates:)
• -insertCoordinates:count:atIndex:
• -removeCoordinatesInRange:
• optionally -appendCoordinates:count:

These operations have tricky edge cases that make our manual use of C memory management particularly perilous: an off-by-one error can go undetected even with unit tests. So I think we should convert the internal representation to use a std::vector instead of a heap-allocated C array: #6580. Once we fix #5201, we’ll need to factor out the implementations of these methods into freestanding C functions to avoid repetition.

/ref #6565 (comment)
/cc @incanus @friedbunny @boundsj @ryanbaumann

[1ec5]

Putting this bug back on the 3.4.0 milestone, because it makes no sense to be able to grow a polyline but not shrink it.

[1ec5]

#6890 (comment) all but spells out the code needed to fix this issue.

[1ec5]

Fixed in #7251 on the v3.4.0 release branch.