Adds support for CldrJSONDataProvider for Dates (based on #256) (#258)

* Add support for Dates to CLDRJsonDataProvider

* Apply feedback

components/cldr-json-data-provider/src/cldr_paths.rs

@@ -10,12 +10,14 @@ pub struct CldrPaths {
     /// Path to checkout of cldr-core:
     /// https://github.com/unicode-cldr/cldr-core
     pub cldr_core: Result<PathBuf, MissingSourceError>,
+    pub cldr_dates: Result<PathBuf, MissingSourceError>,
 }
 
 impl Default for CldrPaths {
     fn default() -> CldrPaths {
         CldrPaths {
             cldr_core: Err(MissingSourceError { src: "cldr-core" }),
+            cldr_dates: Err(MissingSourceError { src: "cldr-dates" }),
         }
     }
 }

components/cldr-json-data-provider/src/reader.rs

@@ -1,11 +1,24 @@
 use crate::error::Error;
+use std::fs;
 use std::fs::File;
 use std::io::BufReader;
-use std::path::PathBuf;
+use std::path::{Path, PathBuf};
 
 /// Helper function to open a file and return failures as a crate error.
 pub fn open_reader(path: PathBuf) -> Result<BufReader<File>, Error> {
     File::open(&path)
         .map(BufReader::new)
         .map_err(|e| Error::IoError(e, path))
 }
+
+/// Helper function which returns a sorted list of subdirectories.
+pub fn get_subdirectories(root: &Path) -> Result<Vec<PathBuf>, Error> {
+    let mut result = vec![];
+    for entry in fs::read_dir(root).map_err(|e| Error::IoError(e, root.to_path_buf()))? {
+        let entry = entry.map_err(|e| Error::IoError(e, root.to_path_buf()))?;
+        let path = entry.path();
+        result.push(path);
+    }
+    result.sort();
+    Ok(result)
+}