fix: Use byte[] instead of String to store stats.json

[TatuLund]

This is made to avoid excessive memory usage when managing the data

fixes: #11515

[vaadin-bot]

SonarQube analysis reported 3 issues

1. FrontendUtils.java#L482: Remove this use of "closeQuietly"; it is deprecated.
2. FrontendUtils.java#L536: Remove this use of "closeQuietly"; it is deprecated.
3. FrontendUtils.java#L168: Do not forget to remove this deprecated code someday.

[vaadin-bot]

Hi @TatuLund and @mshabarov, when i performed cherry-pick to this commit to 2.7, i have encountered the following issue. Can you take a look and pick it manually?
Error Message:
Error: Command failed: git cherry-pick 8412449
error: could not apply 8412449... fix: Use byte[] instead of String to store stats.json (#11516)
hint: after resolving the conflicts, mark the corrected paths
hint: with 'git add ' or 'git rm '
hint: and commit the result with 'git commit'

[vaadin-bot]

Hi @TatuLund and @mshabarov, when i performed cherry-pick to this commit to 2.6, i have encountered the following issue. Can you take a look and pick it manually?
Error Message:
Error: Command failed: git cherry-pick 8412449
error: could not apply 8412449... fix: Use byte[] instead of String to store stats.json (#11516)
hint: after resolving the conflicts, mark the corrected paths
hint: with 'git add ' or 'git rm '
hint: and commit the result with 'git commit'

[TatuLund]

@mshabarov here: #11529

[vaadin-bot]

This ticket/PR has been released with platform 22.0.0.alpha1 and is also targeting the upcoming stable 22.0.0 version.