Failed to enter insert-mode if a snippet starts with a linked placeholder.

To Reproduce

See this simple snippet:

	"test": {
		"prefix": "test",
		"body": [
			"${1:some_placeholder}, $1" 
		],
	},

After typing "test" and expanded, vim enters visual mode instead of insert mode.

The bug occurs only if all 3 conditions below are met:

1. The snippet must start with a placeholder. "blah blah ${1:some_placeholder} $1" works fine.
2. The placeholder must be linked. "${1:some_placeholder} blah blah" works fine.
3. It should be a placeholder, not a simple tabstop. "$1 blah blah $1" works fine.

Environment (please complete the following information):

• Extension (VsCodeVim) version: 1.18.5
• VSCode version: 1.52.1
• OS: win10

Reproduce the supplied snippet in VSCodeVim and trace the snippet-expansion path into the insert/visual-mode transition. Done means a snippet beginning with a linked placeholder enters insert mode rather than visual mode, while the contrasting examples in the report continue to behave as described.