Align iconPath-API

[jrieken]

We have various definitions for iconPath properties and they all have different type signatures (no support ThemeIcon, no support for light/dark). We should always use the same OR-type sausage, ideally: Uri | { light: Uri; dark: Uri } | ThemeIcon.

---

• SourceControlResourceThemableDecorations#iconPath @joao, @eamodio Add ThemeIcon support to SCM decorations #128258
• CommentAuthorInformation#iconPath @rebornix
• CommentReaction#iconPath @rebornix
• WebViewPanel#iconPath Allow ThemeIcon in WebviewPanel.iconPath #90616

[jrieken]

This also needs support from the actual feature area owners

[mjbvz]

#90616 Tracks enabling themeIcons in webviews

[eamodio]

@jrieken should we add decorations to this too?
ThemableDecorationRenderOptions#gutterIconPath
ThemableDecorationAttachmentRenderOptions#contentIconPath

[eamodio]

#128258 tracks SCM decoration ThemeIcon support

[alexr00]

CommentAuthorInformation#iconPath

I think there's an argument that we leave this one as only Uri. This is intended to be a representation of a user. It would be odd if this were a codicon.

[jrieken]

Well, could be the default icon in case no custom user icon exists?

[jrieken]

We have extracted IconPath but there are still a few places where we use slightly different iconPath shapes