tests/rustdoc-json/remap-path-prefix

Tests for --remap-path-prefix and --remap-path-scope with rustdoc JSON:

• remap-path-prefix: only uses bare --remap-path-prefix, expects remapped paths
• doc: pass --remap-path-prefix and the documentation scope, expects remapped paths
• object: pass --remap-path-prefix and the object scope, expects un-remapped paths
• debuginfo: pass --remap-path-prefix and the debuginfo scope, expects un-remapped paths