CommandPalette's keyboard accelerators not read properly sometimes

# Environment

WT version: after #9234 merges

# Steps to reproduce

1. open command palette
2. Navigate focus to a command with ctrl+- keyboard accelerator

# Expected behavior

screen reader reads "control minus"

# Actual behavior

screen reader reads "control plus"

# Suggested approach

https://docs.microsoft.com/en-us/windows/uwp/design/input/keyboard-accelerators

Maybe we need to create `KeyboardAccelerator` objects from the strings we get? This just sounds like the correct approach tbh.

Start at the CommandPalette handling for keyboard accelerator strings, then review the Windows keyboard accelerator guidance linked in the issue. Reproduce the Ctrl-minus command with a screen reader and verify that it announces “control minus” rather than “control plus” after the accelerator handling is corrected.

Written by the indexing model from the issue text.