.Net: [MEVD] Merge old integration tests into the new ones

[roji]

We currently have two integration test suites for MEVD: the older one (under src/IntegrationTests, mainly provider-by-provider), and the new one (under test/VectorData, with cross-provider conformance conformance tests). Go over the older one, merge anything that's missing from the new one, and remove the old one.

[github-actions]

This issue is stale because it has been open for 90 days with no activity.