Text reflow doesn't respect tabs

[aykevl]

When reflowing lines that are indented using tabs (using gq for example), tabs are replaced by spaces.

Steps to reproduce the behavior:

1. Select a few commented lines with Shift V, for example the two commented lines in the following code (note the tabs at the beginning):

   	// Gather the list of parameters for every call we're going to
   	// make.
   	callParams := make([]llvm.Value, call.OperandsCount()-1)
   	for i := range callParams {
   		callParams[i] = call.Operand(i)
   	}

2. Press g q
3. Notice how the line has become the following, with a single space for indentation completely breaking indentation:

    // Gather the list of parameters for every call we're going to make.
   	callParams := make([]llvm.Value, call.OperandsCount()-1)
   	for i := range callParams {
   		callParams[i] = call.Operand(i)
   	}

I would expect this to become like the following:

	// Gather the list of parameters for every call we're going to make.
	callParams := make([]llvm.Value, call.OperandsCount()-1)
	for i := range callParams {
		callParams[i] = call.Operand(i)
	}

Screenshot after reflowing:

Environment:

• Extension (VsCodeVim) version: 1.9.0
• VSCode version: 1.36.1
• OS: Linux (Debian Stretch)

Some settings that might be relevant:

    "window.zoomLevel": 1,
    "editor.fontSize": 13,
    "editor.renderWhitespace": "boundary",
    "vim.searchHighlightColor": "rgba(255, 255, 0, 0.5)",
    "vim.hlsearch": true,
    "editor.wordWrap": "on",
    "editor.wrappingIndent": "deepIndent",
    "editor.minimap.enabled": false,
    "editor.hover.enabled": false,
    "[html]": {
        "editor.tabSize": 2,
    },
    "files.insertFinalNewline": true

I'm testing this with Go, which basically always uses tabs for indentation so this is a real problem for me.