Backpack thumbnail for blocks is broken for RTL languages

[chrisgarrity]

Expected Behavior

Thumbnail of blocks in the backpack should look like a small version of the stack.

Clarifying what should/shouldn't happen when switching between languages:

• Thumbnail should be generated at the time the blocks are added to the backpack.
• The thumbnail should look like the blocks in the current language (i.e. LTR or RTL)
• If you change language, the thumbnail for a saved stack does not change (current behavior)
• When you drag a stack from the backpack to the workspace, it uses the current thumbnail, but when you drop it the blocks appear in the current language. (current behavior)

Actual Behavior

The thumbnail just looks like a vertical line:

Steps to Reproduce

1. Switch into a RTL locale like arabic
2. Drag a stack of blocks into the backpack

Operating System and Browser

Mac OS 10.14.6 Chrome Version 84.0.4147.105 (Official Build) (64-bit)