URI-encoded inline source maps don't work.

Current code expects that all inline source maps are base64-encoded.

PR in https://github.com/Microsoft/vscode-chrome-debug-core/pull/344.

Mostly manifests when using `esm` package.

Referenced in
https://github.com/standard-things/esm/issues/120
https://github.com/Microsoft/vscode/issues/35978#issuecomment-405813306