Allow user to specify file location when prompted "Error: Unable to resolve non-existing file"

Type: Debugger

Describe the bug

• OS and Version: Windows 10
• VS Code Version: 1.43.2
• C/C++ Extension Version: 0.27.0

I am using VS Code to debug a C++ compiled .exe. I can configure a launch.json that successfully launches my .exe. However when I attempt to step into a function I get the following error:

`Unable to open 'thing.cpp'. Unable to read file 'c:\foo\bar\baz'. (Error: Unable to resolve non-existing file 'c:\foo\bar\baz'.

This makes sense. The file does not exist at 'c:\foo\bar\baz' because it was produced by a caching build system. However the file does exist on my hard drive in another location.

In Visual Studio I get a similar prompt. Except Visual Studio lets me specify the file location. This lets me successfully step-into and debug my code. Unfortunately VS Code does not give me this option. The file exists in my VS Code workspace which makes it particularly frustrating.

My feature request: when debugging fails to read the file allow the user to specify the file's location. If a file with the correct filename and similar path offer to open that file automatically.

To Reproduce
Here is a guess at some minimum work.

Clone a C++ repo onto one machine in a location of your choice. Copy the .exe to a different machine that has cloned the same repo into a different location. Configure launch.json to launch your exe. Try to step into some code. It should fail with an error that the file doesn't exist at a specific location. Even though the file does exist on your machine and, ideally, VS Code workspace.

Additional context
In my particular use case I have an .exe and many DLLs. We use a caching build system (Buck) so the DLLs were compiled on a build machine with completely different folder structure. Even though the code used to compile that DLL exists on my machine.

Creating a minimum-repro project for this would take a little work. If that would be useful I can do it. But I think the problem/missing feature here is pretty obvious so I'm not sure it would be worth the effort.

Start by reproducing the missing-source prompt from launch.json while stepping into code built at a different path. Inspect the debugger's handling of unresolved source files and the workspace location; no implementation files or tests are named. Done when a user can choose the local source location and continue stepping into it.