add hello_world example for String and Vec<String>

[sengmonkham]

#1901
This PR adds the hello_world integration test to the Soroban test suite, addressing one of the missing upstream Soroban examples.

[mohamedbasuony]

Thanks for the PR. The checks are still red: DCO is failing and the Linux x86-64 build/test job is also failing. Please sign off the commit and fix the Linux CI failure, then push an update.

[sengmonkham]

@mohamedbasuony Thanks for merging my PR!

Just a quick heads-up: I added the @babel/core dev dependency to vscode/package.json in this PR because the VS Code extension tests were failing in the CI with the following error:

Error [ERR_MODULE_NOT_FOUND]: Cannot find package '@babel/core' imported from /home/runner/work/solang/solang/vscode/node_modules/reghex/src/babel/plugin.test.js

This failure was completely unrelated to the hello_world example but was blocking the CI pipeline. If this was an environment issue on the CI rather than a genuinely missing dependency, please let me know if you'd like me to revert it in a separate follow-up PR!