fixs #2325 Cmd+D loses multiple selections

[redhat008]

What this PR does / why we need it:

Fix the bug. Cmd+D loses multiple selections #2325

Which issue(s) this PR fixes

fixs #2325 Cmd+D loses multiple selections

Special notes for your reviewer:

1. only test in my computer
2. I am a programmer, but not familiar with typescript/js and vscode extension development. Just compare with 0.10 with 0.12 code . the logic have changed ， so produce issue Improve Test Infrastructure #2335

[TravisBuddy]

Hey @redhat008,
Something went wrong with the build.

TravisCI finished with status errored, which means the build failed because something unrelated to the tests, like a problem a dependency or the build process itself.

[xconverge]

I had recently added https://github.com/VSCodeVim/Vim/blob/master/test/multicursor.test.ts

Is there any chance you can add a test without your fix, and then make sure it passes with your fix?

These are tricky issues and I would love to catch them in tests if possible! Thanks

[redhat008]

Sorry. I'm not familiar with typescript/js and vscode extension development. I don't know how to add the test

[jpoon]

You can take a look at our existing tests. For instance:

Vim/test/mode/modeVisual.test.ts

Line 68 in 00c1135

test('Can handle x across a selection', async () => {

f

[xconverge]

The file I linked has 2 other tests, you can just mimic one of them and add it to that file even multicursor.test.ts