Fix paths when running in a codespace or github.dev browser extension

[thegecko]

This PR injects path substitutions to correctly convert file paths in the debugger to those used in VS Code in some web scenarios.

This fixes #89, however this wasn't necessary in the past and it's possible this is working around a recent regression in VS Code and should be fixed there.

If not, it may be better to implement this fix in the underlying DebugSession conversion functions, however this would require knowledge of the current UI file scheme injected from the client somehow.

To recreate the issue, please refer to instructions on the test repo here:
https://github.com/thegecko/vscode-web-test

To help with testing, a duplicate version of the mock-debug extension including these fixes is published here:
https://marketplace.visualstudio.com/items?itemName=arm-debug.mock-debug-test

Tested to be working on:

• VS Code Desktop
• vscode.dev
• Codespaces (Codespace/Remote Extension Host)
• Codespaces (Local/UI Extension Host)
• github.dev