Update mStandby flag in RecordThread

Summary: RecordThread is using mStandby flag to indicate if it's in the standby mode, and sets it to true when there are no active (not silenced) and not paused streams.
Additionally, setting the FastCapture thread to COLD_IDLE state which pauses any processing there.

At some point in time, a track may be unmuted and becomes active again, which changes the state of FastTrack thread to READ_WRITE (active).

Unfortunately, the mStandby flag is not modified accordingly. Currently it's only set to false when new track is starting (different path, than silenced one). This causes RecordThread to end up in situations like one captured below:

```
Input thread 0x795cdc6b00, name AudioIn_B6, tid 29295, type 3 (RECORD):
  I/O handle: 182
  Standby: yes
  Sample rate: 48000 Hz
  HAL frame count: 144
  HAL format: 0x1 (AUDIO_FORMAT_PCM_16_BIT)
  HAL buffer size: 288 bytes
...
  AudioStreamIn: 0x795cca2600 flags 0x1 (AUDIO_INPUT_FLAG_FAST)
  Frames read: 8823951
  Fast capture thread: yes
  Fast track available: yes
  FastCapture command=READ_WRITE readSequence=124589 framesRead=8970336
              readErrors=0 sampleRate=48000 frameCount=144
              measuredWarmup=107 ms, warmupCycles=3 period=3.00 ms
  1 Tracks of which 1 are active
    Active     Id Client Session Port Id  S  Flags   Format Chn mask
    F  yes    131  29016     705     120  A  0x000 00000001 00000010
...
```

Where Standby: yes and FastCapture command=READ_WRITE. This situation
may cause crashes, as RecordThread may modify/remove clients without
notifying the FastCapture thread, because it thinks it's in standby mode and is not
running.


Test: Successful Build on master branch
Test: atest CtsMediaAudioTestCases


Bug: 382396707
Change-Id: I2414f8e26a61a232d3f07d9eea8c22b4931aa55b
Signed-off-by: Abdelrahman Daim <adaim@meta.com>