Improve general test matrix

[bricelam]

Areas

• HasNoKey (keyless entity types) @bricelam
  • On the dependent end of a relationship
  • With data seeding
  • RevEng
• @divega EF6 with EDMX
• ToQuery (defining query) @AndriySvyryd
  • On the dependent end of a relationship
  • With inheritance
  • With table splitting
  • With SaveChanges
  • With FromSql
• Cosmos (nightly build) @smitpatel
  • Nested owned types
  • Container per type
  • Keyless entity types
  • Partition keys
• Set operations @maumar
• CHECK constraints @roji
• Table/column comments @roji
• SQL Azure
• Outer/Cross Apply
• Complex query filters (e.g. containing other dbsets as part of the filter)
• Owned types with lazy loading proxies
• Model snapshot
• Executing migrations

From #17618:

Areas missing automated coverage:

• Core
  • Conventions APIs (possibly just inlined)
• Relational
  • Connection resiliency
• SQL Server
  • Full text search
  • SqlServerDbFunctionsExtensions (client-side)
  • SqlServerUdtTypeMapping
• SQLite
  • Spatial
    • Custom SRIDs
    • Custom Dimensions Sqlite Spatial: Test Z and M #13767
• Design
  • MigrationsScaffolder
  • RevEng
    • Spatial
• Tools

[ajcvickers]

Triage: Moved EF6 issue to dotnet/ef6#1137. The rest we plan to do for 3.1.

[smitpatel]

Tests for Outer/Cross Apply

[maumar]

tests for complex query filters (e.g. containing other dbsets as part of the filter)