[repository] Drop the entities.extid column and associated cache
This was not necessary anymore with promoted usage of the new data import API.
Turn repository's _type_extid_cache to _type_cache with only the entity's type
as key.
This introduces an backward incompatible change: entity_metas dict doesn't
contains anymore the extid key, but it doesn't seem used at all anywhere, so
this sounds acceptable.
Closes #15538317
CSS Coding Standards
--------------------
(Draft, to be continued)
:Naming: camelCase
Indentation rules
~~~~~~~~~~~~~~~~~
- 2 espaces avant les propriétés
- pas d'espace avant les ":", un espace après
- 1 seul espace entre les différentes valeurs pour une même propriété
Documentation
~~~~~~~~~~~~~
Please keep rules semantically linked grouped together, with a comment about
what they are for.
Recommendation
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- Try to use existing classes rather than introduce new ones
- Keep things as simple as possible while in the framework
- Think about later customization by application
- Avoid introducing a new CSS file for a few lines of CSS, at least while the
framework doesn't include packing functionalities