Ignore some regex characters in sourcemap overrides pattern

[msafi]

I'm trying to setup vscode-chrome-debug for our project.

The source map URLs for our projects look like this:

webpack+subproject:///./src/js/actions/accordion.js

So I tried the following

"sourceMapPathOverrides": {
  "webpack+subproject:///./*": "${webRoot}/*"
}

...but that didn't work because the code for the overrides treats the + as part of a regex, which it's not.

I've modified the code in sourceMapUtils.ts to ignore some regex characters in the override URLs. Not sure if that's the right solution, but I hope that at least it illustrates the problem.

(Sorry for mixing in formatting changes there!)

[msftclas]

All CLA requirements met.

[roblourens]

This looks great! I can probably reduce the number of "escape regex chars" util methods I have, and escaping whitespace doesn't seem necessary, but I will work on that. Thanks for the PR.