RelectorHost threw an exception when metadata was requested for a
.d.ts file that didn't have a .metadata.json file. Changed it to
return undefined.
Fixes#9678
Refactored ReflectorHost to allow it to be tested.
Fixed an issue where the .d.ts was findable but it wasn't used by the project
(This happens when the .metadata.json file references a module that was not
needed, such as it doesn't declare any types, and the reference to it was
elided by TypeScript when writing the .d.ts file).
Added tests for ReflectorHost
Victor Berchet
Chuck Jazdzewski
ScottSWu
vsavkin
Alex Eagle