Add "create-or-update-tab" API and executable

[fredemmott]

For example:

create-or-update-tab `
  --type folder `
  --id bms-terrain `
  --title Terrain `
  --glyph E709 `
  --path `C:\falcon\...\MyMap`

Glyph reference: https://learn.microsoft.com/en-us/windows/apps/design/style/segoe-ui-symbol-font - though this isn't straightforward: codepoint to utf-8 conversion was deprecated in C++17, and while OpenKneeboard is UTF-8, we're not guaranteed anything about the encoding of the input.

[fredemmott]

Not going to do this - adding tabs should always be done by the user through the UI. However, may add a 'custom tab' discovery mechanism allowing third-party apps to register a new tab type.