hook_entity_info(), hook_schema(), and the field system are strongly bound to each other

Problem/Motivation

#910190: Entire schema cache needlessly loaded on all pages fixed a performance issue, but introduced a big pain: because entity_get_info() indirectly calls drupal_get_schema() the entity and schema information are intractably bound to each other. Also, because the Field SQL storage needs to query the field information in a hook_schema(), the field system is also intractably bound to the two others.

This means that:

1. In hook_entity_info() and hook_entity_info_alter(), you cannot call either drupal_get_schema() nor field_info_field()
2. In hook_schema(), hook_schema_alter and hook_field_schema(), you cannot call either entity_get_info() nor field_info_field()
3. In hook_field_extra_fields(), you cannot call either entity_get_info() nor drupal_get_schema()

Three example cases:

• This prevents the UUID module from adding a column to the schema of the base table of an entity based on the entity info; at least not without an ugly workaround;
• This prevents Drupal Commerce from adding a view mode to an entity based on the fields that point to it; at least not without an ugly workaround;
• This prevents the Entity Reference module from adding foreign key information to its fields pointing the the base table of the target entity table; at least not without an ugly workaround.

Proposed resolution

We modify entity_get_info() only compute the schema *after* the computing of the entity info is complete (minor API change, see below).

User interface changes

None.

API changes

The SQL schema information is not available anymore in hook_entity_info_alter().