Convert FilteredFileReader to use FileSpec

Summary: FilteredFileReader and its Meta-only relative, FilteredVRSFileReader, are converted to use FileSpec instead of working only with a string path. This makes a number of operations less awkward, but more importantly, it makes working with file variations easier (further diffs).

Reviewed By: kiminoue7

Differential Revision: D45381009

fbshipit-source-id: f829b69a4391578962b23d59bd597eded374582f

src/experimental/main.cpp

@@ -127,7 +127,7 @@ int main(int argc, const char* argv[]) {
   vrs::utils::FilteredFileReader filteredReader;
   // Initialize VRS Reader and filters
   filteredReader.setSource(vrsPathIn);
-  filteredReader.reader.openFile(filteredReader.path);
+  filteredReader.openFile();
   filteredReader.applyFilters({});
 
   // Configure Copy Filter and initialize the copy