Unicode 'BACKSPACE' stop to read project

[yokobond]

Expected Behavior

Should be open and run project in v3 as v2.

Actual Behavior

If a project contains Unicode character 'BACKSPACE' (\u0008), it will not run on Scratch 3.0 beta. The scripts are disappeared after the character and not editable in v3.0 any more.

Steps to Reproduce

Unicode Character 'BACKSPACE' (\u0008)

Unicode Character 'BACKSPACE' (\u0008) on Scratch 3.0 beta

Operating System and Browser

MacOS 10.13.6
Chrome 70.0.3538.110

[apple502j]

Related to #3871 , scratchfoundation/scratch-vm#1077 , LLK/scratch-blocks##1822
However, this should be tagged as critical and fixed before the release, since it will affect for most of Mac users.

[apple502j]

To reproduce this, you need to type in Japanese input method.
It only happens with MacOS.

1. type some character into 2.0's string argument
2. press Space (to execute IME)
3. BEFORE PRESSING ENTER KEY, press Delete
4. Done.

[thisandagain]

Moved to scratchfoundation/scratch-vm#1873