[Ctrl]+[D] adjacent text extends selection instead of selecting seperately

[martin-sweeny]

• VSCode Version: 1.8.0-insider
• OS Version: Windows 10

Steps to Reproduce:

1. Type aaaaa
2. Select the first character
3. Press Ctrl+D several times

Expected Behaviour:

• The editor will select the following occurrences of a until all individual a's are selected.

Actual Behaviour:

• The editor adds the following a to the current selection on each time that Ctrl+D is pressed. This means that the second time, you are not selecting the next occurrence a but aa and the third time you are adding aaaa to your selection

This is important. A common use case would be when you want to change the characters individually, or when you want to add characters in between them.

With Sublime, you can select all the characters (individually) as expected:

With VS Code, you can't even select them all, and it's one long selection (rather than several distinct ones):

[alexdima]

Dup of #11150