Improves the build output:

1. Gives confirmation that the build succeeded
2. Gives the path to the built executable

This matches the behavior of other Flutter platforms like Android.

Part of #120127

Flutter run

> flutter run -d windows
Launching lib\main.dart on Windows in debug mode...
Building Windows application...                                    11.1s
✓  Built build\windows\runner\Debug\x10.exe.
Syncing files to device Windows...                                  60ms

Flutter run key commands.
r Hot reload. 🔥🔥🔥
R Hot restart.
h List all available interactive commands.
d Detach (terminate "flutter run" but leave application running).
c Clear the screen
q Quit (terminate the application on the device).

Flutter build

> flutter build windows
Building Windows application...                                    25.9s
✓  Built build\windows\runner\Release\x10.exe (0.1MB).

Pre-launch Checklist

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

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