[source_span] Preserve symmetric SourceSpan equality and add FileSpan equality tests

pkgs/source_span/lib/src/file.dart

diff --git a/pkgs/source_span/lib/src/file.dart b/pkgs/source_span/lib/src/file.dart
index 6de8484..8aa5814 100644
--- a/pkgs/source_span/lib/src/file.dart
+++ b/pkgs/source_span/lib/src/file.dart
@@ -388,14 +388,12 @@
     if (other is _FileSpan) {
       return _start == other._start &&
           _end == other._end &&
-          sourceUrl == other.sourceUrl &&
-          (file == other.file || text == other.text);
+          sourceUrl == other.sourceUrl;
     }
     if (other is SourceSpan) {
       return _start == other.start.offset &&
           _end == other.end.offset &&
-          sourceUrl == other.sourceUrl &&
-          text == other.text;
+          sourceUrl == other.sourceUrl;
     }
     return false;
   }

pkgs/source_span/test/file_test.dart

diff --git a/pkgs/source_span/test/file_test.dart b/pkgs/source_span/test/file_test.dart
index e51d61b..5b957e1 100644
--- a/pkgs/source_span/test/file_test.dart
+++ b/pkgs/source_span/test/file_test.dart
@@ -533,5 +533,31 @@
         });
       });
     });
+
+    group('equality', () {
+      test('two FileSpans with the same offsets and URL are equal', () {
+        final span1 = file.span(5, 12);
+        final span2 = file.span(5, 12);
+        expect(span1, equals(span2));
+        expect(span1.hashCode, equals(span2.hashCode));
+      });
+
+      test('FileSpan and SourceSpan equality is symmetric', () {
+        final fileSpan = file.span(5, 12);
+        final sourceSpan = SourceSpan(SourceLocation(5, sourceUrl: 'foo.dart'),
+            SourceLocation(12, sourceUrl: 'foo.dart'), 'other!!');
+        expect(fileSpan == sourceSpan, isTrue);
+        expect(sourceSpan == fileSpan, isTrue);
+      });
+
+      test('FileSpans with different offsets or URLs are not equal', () {
+        final span = file.span(5, 12);
+        expect(span, isNot(equals(file.span(6, 12))));
+        expect(span, isNot(equals(file.span(5, 11))));
+        final otherFile =
+            SourceFile.fromString('foo bar baz\nwhiz bang boom', url: 'b.dart');
+        expect(span, isNot(equals(otherFile.span(5, 12))));
+      });
+    });
   });
 }