[datlechin]

Summary

• Cell menu of a table tab: Open Referenced Row (Ctrl+J, listed in the shortcuts dialog) on a foreign key cell, and Show Referencing Rows on a saved row, one item per key pointing at it.
• The rows open in a new tab beside the source tab, filtered on every column of the key with the filter strip shown. A tab already showing those rows comes to the front. A NULL key offers nothing.
• A column in several keys gets a submenu of table (columns) items, the key's own columns, with the constraint added when two keys from the same columns clash; Ctrl+J offers the same choices at the cell. A key that cannot be followed says why in a toast. A table missing from its schema, read again from the server first, says so instead of opening.
• Keys between neighbouring types follow: a decimal key is written without its scale's zeros, a real key as the double it widens to, and a filter compares a date with a timestamp's midnight and back.
• New Connection::fetch_inbound_foreign_keys on every driver, sharing the SQL fetch_table_definition runs. The browse tab reads its keys with its columns; a failure never fails the tab and is asked again on the next connection.
• A table tab keeps its own filter in the saved workspace and through Reopen Closed Tab. A followed filter does not replace the table's remembered one until the user applies a filter.
• Filters compare binary columns to a 0x hex value, and the filter strip lists binary columns.
• The saved tabs keep at most 256 KiB of filters, so a filter from a large binary key cannot make the workspace file too large to read back.
• PostgreSQL: the partition clones of a foreign key are no longer listed as keys, outbound or inbound.
• SQL Server: filters compare text, ntext and image columns cast to their max types, which =, <> and IN need.
• SQLite: a key's table and columns come back as the parent declares them, not as the REFERENCES clause spelled them. A key to a missing table no longer fails the read of every key of the table. Show Referencing Rows refuses, with a toast, a key whose parent columns compare under another affinity or collation than the child's, where = would miss rows or add some.
• One shared ui::menu_label replaces the two copies in the picker and the structure tab.
• Tests changed on purpose: a_filter_on_a_binary_column_reads_the_hex_form_an_export_writes (was ..._compares_text), add_rule_appends_a_row_for_the_first_column and set_columns_rebuilds_the_column_choices now expect a binary column in the strip; a_blob_is_not_filterable is removed with is_filterable.

Test plan

• Core: RowReference (composite keys, NULL, empty text, blobs, uneven keys, unknown schema, decimal and real keys), hex decode, binary filter parse and bind, date and timestamp comparison.
• SQLite: declared spellings both ways, a key to a missing table, inbound keys read alone equal the definition's, blob equality.
• PostgreSQL, MySQL/MariaDB, SQL Server (docker, run here): inbound keys read alone, partition clones dropped, bytea, varbinary, image, text and ntext equality, the DDL conformance cases that read keys back.
• Grid: menu items per cell, submenu for two keys, referencing rows skip drafts, refusal toast, Ctrl+J with one key and with two.
• Browse tab: keys read with the columns and again after a reconnect, followed filter kept off the table's store, strip revealed.
• Workspace: opens beside the source, reveals an open tab, toasts a missing table, saved record and reopen keep the filter, the filter budget.
• verify.sh build, test, lint and the CI fast job's meson test in the dev container.

Fixes #3671