Improve many-to-many, skip navigations, and indexer properties

[ajcvickers]

This is a grouping of related issues. Feel free to vote (👍) for this issue to indicate that this is an area that you think we should spend time on, but consider also voting for individual issues for things you consider especially important.

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This an "epic" issue for the theme of improvements to many-to-many and the constructs from which it is composed. Specific pieces of work will be tracked by linked issues.

Done in 6.0

• Detect simple join tables in reverse engineering and create many-to-many relationships #22475
• Support unidirectional many-to-many relationships #3864

Backlog

• Perf testing for many-to-many #21919
• Indexer Navigations #13729
• Model "implicit" many-to-many scenarios via readonly navigations (no join table) #20337
• Support non-many-to-many skip navigations #21673
• Create an alternate key for join entity types which have an independent PK #21900
• Determine how to look up join entity types at model building time #21901
• Use simple entity type for simple join tables #22000
• Improve the query generated for many-to-many explicit/lazy load #22022