DASH-1281 block_dash: add "Hide suspended users" condition

[stefanscholz]

The users data source excludes deleted users (u.deleted = 0) but still lists suspended accounts, with no way to filter them out. This adds an opt-in condition — "Hide suspended users" — that restricts results to u.suspended = 0.

Behaviour

Off by default, like every other Dash condition. abstract_data_source::before_data() removes any filter whose preferences[filters][<name>][enabled] is falsy (and removes all filters when no filters preference exists at all), so existing block instances are unaffected until someone ticks the box on the block's Conditions tab.

Block state	SQL	Suspended user
Fresh, no saved preferences	no u.suspended clause	visible
Condition explicitly disabled	no u.suspended clause	visible
Condition enabled	u.suspended = :hide_suspended_users	hidden

Notes

• get_operation() returns OPERATION_EQUAL rather than the inherited OPERATION_IN_OR_EQUAL. The latter routes through $DB->get_in_or_equal(), which names its placeholder from a process-wide counter (param1, param2, …), making the emitted SQL depend on how many unrelated DML calls preceded it. OPERATION_EQUAL yields the stable u.suspended = :hide_suspended_users.
• Registered outside the block_dash_has_pro() guard, so it is available (and unit-testable) without local_dash.
• version.php bumped to refresh the lang-string cache on upgrade. No db/upgrade.php savepoint — this is not a DB upgrade.

Tests

New tests/hide_suspended_users_condition_test.php covers the generated SQL and params, that the condition is registered on the users data source but disabled by default, and that suspended users drop out of the result set only once it is enabled.

Follow-up (not in this PR)

Conditions do not propagate — each data source hard-codes its own set in build_filter_collection(). Wiring this into the local_dash addon data sources is a separate ticket. Two of them need care: calendar_events LEFT JOINs {user} on ce.userid (0 for site/course/category events) so it would need a null-safe (u.id IS NULL OR u.suspended = 0), and badges LEFT JOINs {user} pinned to $USER->id, so u is the viewer rather than the row subject and the condition would be meaningless there.