Add progress reporting to PortablePdbWriter

[andrewcrawley]

Problem

As discussed in #2801, the Visual Studio debugger would like to be able to provide better progress feedback to users while a decompilation operation is in progress.

Solution

This commit adds a new parameter to PortablePdbWriter.WritePdb that allows the caller to provide an implementation of IProgress<> to receive status updates on the pdb generation process. Currently, the progress reports include the number of files generated so far and the total number of files.

#2801 mentions adding progress reporting to WholeProjectDecompiler as well, but that appears to already be present - see: https://github.com/icsharpcode/ILSpy/blob/master/ICSharpCode.Decompiler/CSharp/ProjectDecompiler/WholeProjectDecompiler.cs#L256

• At least one test covering the code changed

[siegfriedpammer]

@andrewcrawley thank you for providing the implementation. I have generalized and extended progress reporting in our code base... I hope that you are OK with the changes.

This PR now also implements cancellation of PDB generation in ILSpy and some visual changes:

The size of the progress bar was increased:

Progress now shows more information when exporting a project:

Progress reporting for PDB generation:

[andrewcrawley]

The changes look great, thank you! I was hesitant to wander too far from my original proposal : )

Is there a roadmap for the final release of 8.0, or any info you could share on when that might be?

[christophwille]

No, there is no roadmap and/or timeline for 8.0. Most likely we will have a preview3 late this year, followed by again most likely a couple of RCs. Guesstimate: late winter/early spring next year.