Add public access to a SourceFile's code units (dart-archive/source_span#93)

* Add public access to a SourceFile's code units

This makes it possible to efficiently reparse information from around
a `FileSpan`, such as to expand it through surrounding whitespace
characters. Otherwise, a caller would have to call `getText()` which
can be very expensive in a tight loop.

* Fix lints

* Update CHANGELOG.md

Co-authored-by: Devon Carew <[email protected]>

---------

Co-authored-by: Devon Carew <[email protected]>

Author: nex3

pkgs/source_span/CHANGELOG.md

@@ -1,5 +1,6 @@
-## 1.9.2-dev
+## 1.10.0
 
+* Add a `SourceFile.codeUnits` property.
 * Require Dart 2.18
 * Add an API usage example in `example/`.
 

pkgs/source_span/lib/src/file.dart

@@ -32,7 +32,15 @@ class SourceFile {
   /// the file.
   final _lineStarts = <int>[0];
 
-  /// The code points of the characters in the file.
+  /// The code units of the characters in the file.
+  ///
+  /// If this was constructed with the deprecated `SourceFile()` constructor,
+  /// this will instead contain the code _points_ of the characters in the file
+  /// (so characters above 2^16 are represented as individual integers rather
+  /// than surrogate pairs).
+  List<int> get codeUnits => _decodedChars;
+
+  /// The code units of the characters in this file.
   final Uint32List _decodedChars;
 
   /// The length of the file in characters.

pkgs/source_span/pubspec.yaml

@@ -1,5 +1,5 @@
 name: source_span
-version: 1.9.2-dev
+version: 1.10.0
 description: >-
   Provides a standard representation for source code locations and spans.
 repository: https://github.com/dart-lang/source_span