Noticed all these while prepping for Build:
* Promotes the stabilized features out of `experimental.`
* fixes a bug where a nested command with a `name` would match to a
`renameWindow` action, instead of a command.
* Adds the tab theme icon style
* fixes a bug where `ScrollToMarkAction` wasn't in the list of possible
args, so they would incorrectly get flagged as `moveTab`
* outright adds `experimental.rightClickContextMenu` which was missing
(?)
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