Cast sprite names in one place before passing to getSpriteTargetByName

[ktbee]

Expected Behavior

All blocks should be able to get a sprite target when passing a name if the sprite exists.

Actual Behavior

If the sprite name is a number, it might not be able to find the sprite. getSpriteTargetByName expects a string, and if a block doesn't cast a name to a string, the sprite target can't be found. We should cast the name to a string in one place instead of multiple times in individual blocks.

Steps to Reproduce

See #1743 for repro steps and more details

[ktbee]

@mzgoddard I assigned you this issue since I know this is something you wanted to tackle in your optimization work.