fix(sumo): allow all utf-8 characters via traci

[kschrab]

Description

This PR fixes a bug in the StringTraciWriter class which failed to send a string if it contained at least one UTF-8 character which is represented by more than one byte. To support all characters of the UTF-8 standard, which include characters of Arabic, Chinese, Hebrew, Japanese, Turkish, but also emoji characters, a simple fix in StringTraciWriter has been made, which now sends the length of the encoded byte array rather than the number of characters in the String via TraCI.

Definition of Done

Prerequisites

• You have read CONTRIBUTING.md carefully.
• You have signed the Contributor License Agreement.
• Your GitHub user id is linked with your Eclipse Account.

Required

• The title of this merge request follows the scheme type(scope): description (in the style of Conventional Commits)
• You have assigned a suitable label to this pull request (e.g., enhancement, or bugfix)
• origin/main has been merged into your Fork.
• Coding guidelines have been followed (see CONTRIBUTING.md).
• All checks on GitHub pass.
• All tests on Jenkins pass.

Requested (can be enforced by maintainers)

• New functionality is covered by unit tests or integration tests. Code coverage must not decrease.
• If a bug has been fixed, a new unit test has been written (beforehand) to prove misbehavior
• There are no new SpotBugs warnings.

Special notes to reviewer