(insert) VISUAL mode is not supported

[kgfly]

Describe the bug
(insert) VISUAL mode is not supported

To Reproduce
Steps to reproduce the behavior:

1. When in insert mode, use mouse to select text.
2. Press y to copy

Expected behavior
In normal vim, the text is copy to clipboard.

Observed behavior
The character, y, is inserted and replace the selected text.

Environment (please complete the following information):

• Extension (VsCodeVim) version: 1.28.2
• VSCode version:v.0.16.12
• OS: Ubuntu 18 LTS

Additional context
Add any other context about the problem here.

[kgfly]

If it requires lots of works, could this be simpler?

When using mouse to select text in insert mode, automatically change to visual mode instead of keeping in insert mode.

This is what Visual Studio IDE Vim plugin is doing.

[kgfly]

The missing feature makes very inconvenient when using mouse.