Number fields should not accept non-number characters(ex. Japanese)

[champierre]

Expected Behavior

Number fields should not accept non-number characters like Japanese.
Changing the background color of number fields to red is good UI(see how "point in direction" block behaves in the gif animation) because the user will notice that he/she made mistype.

Actual Behavior

Number fields of any block except "point in direction" accept non-number characters like Japanese.

This is especially bad if user input full-width number(https://en.wikipedia.org/wiki/Halfwidth_and_fullwidth_forms) because it is hard to notice the error.

Ref.
Scratch 2 behaves correctly. Number fields do not accept Japanese.

Steps to Reproduce

• Place any block that has number input field like "move steps" or "turn degrees".
• Input Japanese characters in the input field.

Operating System and Browser

Mac OS 10.14.2 Chrome 71.0.3578.98

[thisandagain]

/cc @picklesrus @chrisgarrity