FTS table detection should be part of .inspect()

[simonw]

The code that detects if specific tables have a corresponding FTS column is currently called from TableView - it should instead be handled as part of .inspect(). This will make it easier to build other features that need to behave differently depending on whether a table can be searched, e.g. an autocomplete widget for selecting filters from foreign key tables.

Current code:

datasette/datasette/app.py

Lines 728 to 733 in f188cea

	# _search support:
	fts_table = None
	fts_sql = detect_fts_sql(table)
	fts_rows = list(await self.execute(name, fts_sql))
	if fts_rows:
	fts_table = fts_rows[0][0]