Support partly migrating patch resource

[ms-henglu]

Versions

the latest

Problem Statement

Here's an example of this case:

1. User use patch resource to manage properties {P1, P2}
2. P1 is now supported in azurerm resource, so there might be plan-diff
3. Currently, since P2 is not supported, this resource can't be migrated,

Expected User Experience

There's no plan-diff.

Proposal

Migrate patch resource partly. In above example, only migrates P1 and P2 stays in the patch resource.

References

[ms-henglu]

The difficulty is that it's hard to remove some properties from patch resource without modifying the rest, which means it's hard to keep the reference/variable usage in the remained properties.

Other options:

1. Let user remove the plan-diff properties manually and fix the config to match state.