Assistant: When Data Viewer is active, include its data and metadata as context

When a text file is open in the active editor, it is automatically included as context in Assistant.

However, if the Data Viewer is the active editor, nothing is automatically included as context.

This makes it difficult to ask Assistant about the data that's right in front of you. When a data viewer is the active editor, we could attach an implicit context object (as we do for files and consoles). This object could contain:

• information for the model about the shape of the data
• some of the data itself
• if the data is in an R or Python session, the identifier of the session and the variable name
• if the data is from a connection, information about the connection
• if the data is from a CSV file, the location of the CSV file and perhaps a sample thereof
• (and so on, i.e. the provenance of the data)
• enough information to perform tool calls to get more more complete data (e.g. getTableSummary)

Start by tracing how Assistant currently attaches implicit context for active files and consoles, then inspect the Data Viewer path and the getTableSummary tool mentioned in the issue. Done should mean an active Data Viewer supplies useful data shape, sample, and provenance context, with enough information for more complete data tool calls.