Launch configs: resolve replacement patterns in object keys, in addition to values

[roblourens]

From https://github.com/Microsoft/vscode-chrome-debug/issues/226

A chrome-debug config can have

            "sourceMapPathOverrides": {
                "webpack:///C:/Depot/Impakt/DNA/DNACore/*": "${webRoot}/*" // SUCCEEDS
                //"webpack:///${workspaceRoot}/*": "${webRoot}/*" // FAILS
                //"webpack:///${webRoot}/*": "${webRoot}/*"  // FAILS
            },   

vscode replaces ${workspaceRoot} in values, and the adapter replaces ${webRoot} in values, and now after microsoft/vscode-chrome-debug#543, in keys as well. It would be great if vscode would replace ${workspaceRoot} in keys.

One issue is that you can have collisions where two keys are the same after applying these replacements. In chrome-debug now, the last one wins where "last" is technically undefined.

[weinand]

duplicate of #34059.
I've just raised the priority of this to "On Deck".