lints 2.0 fixes

In anticipation of lints v 2.0.

(Note the ignores -- I was leery of making API changes but happy to with some guidance.)

See: https://dart-review.googlesource.com/c/sdk/+/237746

Change-Id: I93323e912911bbd62a583b379f0f8140a8ca448d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/237764
Reviewed-by: Ben Konyi <bkonyi@google.com>
Commit-Queue: Phil Quitslund <pquitslund@google.com>

pkg/vm_snapshot_analysis/lib/ascii_table.dart

@@ -102,7 +102,7 @@ class Text {
   String render(int width) {
     if (value.length > width) {
       // Narrowed column.
-      return value.substring(0, width - 2) + '..';
+      return '${value.substring(0, width - 2)}..';
     }
     switch (direction) {
       case AlignmentDirection.left:

pkg/vm_snapshot_analysis/test/utils.dart

@@ -91,7 +91,7 @@ stderr: ${result.stderr}
   });
 }
 
-late final shouldKeepTemporaryDirectories =
+final shouldKeepTemporaryDirectories =
     Platform.environment['KEEP_TEMPORARY_DIRECTORIES']?.isNotEmpty == true;
 
 Future withTempDir(Future Function(String dir) f) async {