function to symmetrize shape keys (similar to weight painting symmetrical bones)

Hi:

I'd like to propose a function to symmetrize shape keys, similar to what blender already does for weight painting bones, so that when we edit shapekey.L , shapekey.R is automatically updated and mirrors shapekey.L.

Currently, to create a mirrored shape keys, we need to duplicate the existing one, then mirror it. However, when we need to make symmetrical changes, we need to delete the mirrored shape key and repeat the above process.

Mirrored shape keys can also be created by choosing left and right vertex groups . However, the the same goes with this method. When we make changed to one side, we need to delete the other shape key and create it again.

Also this method adds complicity to the work flow, because we might want to add another vertex group to it.

(ex. I want my shape keys to only affect the "eye" vertex group, but also have a mirrored version for both left and right. I will need to create a symmetrical shape key with "eye", create new shape key from mix, then choose the left and right vertex groups. if I need to make changes, I might have to repeat the whole process again. )

I think adding a symmetrize function to shape keys can greatly improve our workflow with shape keys, especially for character animators, as a lot of the shape keys we work with are symmetrical.

Thanks!