Hierarchical Context Signalling (OSC 3008) handling

[kruton]

Handle UAPI.15 OSC 3008: Hierarchical Context Signalling. Use cases from the linked document:

Terminal emulators can use hierarchical context information:

• To introduce markers/bookmarks in the output that the user can jump between.
• To visually identify output from different contexts. For example the background of the associated output can be tinted in a reddish tone when privileges are acquired, and similar.
• Meta information on specific output can be shown in a tooltip or similar
• Programs (and all subcontexts) can be killed via a right-click menu on the output they generate.
• Similar, a right-click menu might offer an item to offer opening a new interactive shell in the same working directory that was current on the selected context.
• Failed commands or aborted sessions can be marked requesting user attention.
• A “breadcrumb” style display can be implementing shown the nesting of contexts to the user.