Cannot map Function / F-keys with vim.insertModeKeyBindings

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Is this a BUG REPORT or FEATURE REQUEST? (choose one):
BUG REPORT

Environment:

• VSCode Version: 1.14.2
• VsCodeVim Version: 0.9.0
• OS: macOS 10.12.6

What happened:

1. Set up this keybinding:

    "vim.insertModeKeyBindings": [
        {
            "before": ["<F1>"],
            "after": ["<Esc>"]
        }
    ]

2. Enter insert mode on a file
3. Press F1
4. You remain in insert mode

What did you expect to happen:
Exit insert mode back to normal mode.

How to reproduce it:
See above. This is supposed to be the equivalent of:

map!   <F1>   <Esc>

I don't see function keys handled here, so I'm not sure if it's currently possible to map them: https://github.com/VSCodeVim/Vim/blob/eae183596104d820ca2f87a1934d7a03097dd32c/src/notation.ts#L6

Start by reading src/notation.ts at the linked location to see how key notation is parsed and whether Function/F-key names are represented. Trace the insertModeKeyBindings path for the reported before/after mapping, then verify that pressing F1 exits insert mode as expected.