Add progress bar to artifact downloads (flutter#182836)

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Follow-up to flutter#181808
Resolves flutter#14268

Adds a new `DownloadProgress` class that contains the logic for tracking
and formatting download progress, i.e., a progress bar, % display,
download speed, and ETA.

The rest is mostly ANSI control logic.

Bumped the width of the lines to 80 characters. 

Before:
<img width="799" height="716" alt="image"
src="https://github.com/user-attachments/assets/f479b1b4-bb2b-4c90-bec4-125fba805270"
/>

After:
<img width="886" height="747" alt="image"
src="https://github.com/user-attachments/assets/99e08a23-df7f-4aa3-8945-40bc1be13e4a"
/>


## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [ ] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

---------

Co-authored-by: Ben Konyi <bkonyi@google.com>

Author: Mr-Pepe

packages/flutter_tools/lib/src/base/logger.dart

@@ -10,7 +10,7 @@ import 'package:meta/meta.dart';
 import '../convert.dart';
 import 'common.dart';
 import 'io.dart';
-import 'terminal.dart' show OutputPreferences, Terminal, TerminalColor;
+import 'terminal.dart' show AnsiTerminal, OutputPreferences, Terminal, TerminalColor;
 import 'utils.dart';
 
 const kDefaultStatusPadding = 59;
@@ -1404,7 +1404,7 @@ class AnonymousSpinnerStatus extends Status {
     assert(_timer != null);
     assert(_timer!.isActive);
     if (_terminal.supportsColor) {
-      _writeToStdOut('\r\x1B[K'); // go to start of line and clear line
+      _writeToStdOut(AnsiTerminal.clearAndReturnCode);
     } else {
       _clear(_currentLineLength);
     }

packages/flutter_tools/lib/src/base/terminal.dart

@@ -197,6 +197,10 @@ class AnsiTerminal implements Terminal {
   // Clear the entire line, cursor position does not change.
   static const clearEntireLineCode = '\u001b[2K';
 
+  // Move cursor to column 0 and erase from cursor to end of line (\x1B[K = \x1B[0K).
+  // Clears the entire current line regardless of cursor position.
+  static const clearAndReturnCode = '\r\x1B[K';
+
   static const _colorMap = <TerminalColor, String>{
     TerminalColor.red: red,
     TerminalColor.green: green,