Look up previous builds during codeflow reconstruction

[premun]

Context

During code flow, we sometimes need to recursively reconstruct a previous code-flow because of a conflict.
In this case we re-do the previous flow.
In #4166, we started also storing which build was flowing and so now we can re-construct the flow fully and update version files appropriately.

Goal

• Look up the previous build that was flown in the flow we're reconstructing. Example place in code where this needs to happen:

  arcade-services/src/Microsoft.DotNet.Darc/DarcLib/VirtualMonoRepo/VmrForwardFlower.cs

  Lines 315 to 316 in c64a725

  	// TODO (https://github.com/dotnet/arcade-services/issues/4166): Find a previous build?
  	new Build(-1, DateTimeOffset.Now, 0, false, false, lastLastFlow.SourceSha, [], [], [], []),

  (but generally around places where we deal with PatchApplicationFailedException).
• Disable conflict resolution in such case, as merging the target branch would prevent to apply the current flow on top of the just reconstructed one.

Notes

More on the reconstruction can be seen here: https://github.com/dotnet/arcade/blob/main/Documentation/UnifiedBuild/VMR-Full-Code-Flow.md#conflicts