Emit multiple deltas for a project with multiple baselines

[tmat]

Enables scenario where a shared library Lib is references by multiple executable projects A and B and Lib.dll is copied to their respective output directories and the following events occur:

1. A is launched, modules A.exe and Lib.dll [1] are loaded.
2. Change is made to Lib.cs and applied.
3. B is launched, which builds new version of Lib.dll [2], and modules B.exe and Lib.dll [2] are loaded.
4. Another change is made to Lib.cs and applied.

At this point we have two baselines for Lib: Lib.dll [1] and Lib.dll [2], each have different MVID.
We need to emit 2 deltas for the change in step 4:

• one that chains to the first delta applied to Lib.dll, which itself chains to the baseline of Lib.dll [1].
• one that chains to the baseline Lib.dll [2]

Both of these deltas are sent to the debugger, which applies them to all processes.

Fixes https://devdiv.visualstudio.com/DevDiv/_workitems/edit/2308982,https://devdiv.visualstudio.com/DevDiv/_workitems/edit/2309003

[tmat]

@davidwengier ptal