Categorise test cases into test suite(s)

[cskeogh]

Thank you for the great extension!

I think the vscode-meson should categorise test cases into test suite(s), if exists.

Steps:

1. I am using vscode-meson v1.24.0 with a C/C++ project (gtk)
2. Select VSCode's "Testing" feature from the Activity Bar
3. Observe a long list of test cases. The gtk project categorises the Meson test cases into Meson test suite(s). I think vscode‑meson should categorise too.