Reland "[lldb][progress][NFC] Add unit test for progress reports" (#80791)

This file was previously approved and merged from this PR:
https://github.com/llvm/llvm-project/pull/79533 but caused a test
failure on the Linux AArch64 bots due to hitting an assertion that
`Debugger::Initialize` was already called.

To fix this, this commit uses the
changes made here: https://github.com/llvm/llvm-project/pull/80786 to
use a shared call_once flag to initialize the debugger.