[meta] Stop relying on database schema info at runtime

The root cause [IIRC] for introducing SchemaCache (or rather its D7 equivalent) was

Avoid to load .install files, because they can be big, and we need the table schema info all over the place.

— But in D8, database table schema information should not be needed anymore.

Only the installer + module install/uninstall should need it. In addition, work is actively ongoing to remove schema definitions for entity type base tables from hook_schema() and derive that info from the base field definitions instead.

→ Drop the schema cache altogether and just simply load the .install file of the requested module + invoke its hook_install() at all times.

→ Convert schema.inc into a trivial new Schema class/service.

The primary blockers/offenders are:

1. drupal_write_record() (calls)
2. drupal_get_schema($table) (calls)
3. drupal_schema_fields_sql() (calls)

For (1), I created #1774104: Replace all trivial drupal_write_record() calls with db_merge() a very long time ago already, because drupal_write_record() is definitely replaced by all the (base) field work in D8.

The vast majority of calls to (2) are tests.

The calls to (3) are almost exclusively originating from Entity/Field code. @tstoeckler + @andypost + Co are currently working to fill in some last remaining gaps in that space, with the goal of completely replacing hook_install() for all entity types, since the information can be derived from base field definitions.

Instead of a manually curated table here, please refer to the list of child issues in the sidebar →