[lldb] Enable chaining multiple scripted frame providers per thread (#172849)

This patch allows threads to have multiple SyntheticFrameProviderSP
instances that chain together sequentially. Each provider receives the
output of the previous provider as input, creating a transformation
pipeline.

It changes `Thread::m_frame_provider_sp` to a vector, adds provider
parameter to SyntheticStackFrameList to avoid calling back into
`Thread::GetFrameProvider()` during frame fetching, updated
`LoadScriptedFrameProvider()` to chain providers by wrapping each
previous provider's output in a `SyntheticStackFrameList` for the next
provider and finally, loads ALL matching providers in priority order
instead of just the first one.

The chaining works as follows:
```
  Real Unwinder Frames
      ↓
  Provider 1 (priority 10) → adds/transforms frames
      ↓
  Provider 2 (priority 20) → transforms Provider 1's output
      ↓
  Provider 3 (priority 30) → transforms Provider 2's output
      ↓
  Final frame list shown to user
  ```

This patch also adds a test for this (test_chained_frame_providers) to verify that 3 providers chain correctly: `AddFooFrameProvider`, `AddBarFrameProvider`, `AddBazFrameProvider`.

Signed-off-by: Med Ismail Bennani <ismail@bennani.ma>
GitOrigin-RevId: 17b01bbc67c484068e174d9e9a80089102bea0e8