Rename EstimateTCXNoiseLevel_ivas_fx()
# Bug description
The function `EstimateTCXNoiseLevel_ivas_fx()` should be renamed to `EstimateTCXNoiseLevel_fx()` and the function header should be aligned.
```
/*-----------------------------------------------------------*
* EstimateTCXNoiseLevel()
*
* Estimate and quantize noise factor *
*-----------------------------------------------------------*/
static void EstimateTCXNoiseLevel_ivas_fx(
Encoder_State *st, /* i : encoder state handle */
Word32 x_orig[], /* i : shaped MDCT spectrum Q(31-x_orig_e) */
Word16 x_orig_e, /* i : shaped MDCT spectrum exponent */
Word32 spectrum[], /* i/o: quantized MDCT spectrum */
const Word16 gain_tcx, /* i : global gain Q(15-gain_tcx_e) */
const Word16 gain_tcx_e, /* i : global gain exponent */
const Word16 L_frame, /* i : frame length */
const Word16 noiseFillingBorder, /* i : noise filling border */
const Word16 hm_active, /* i : flag indicating if the harmonic model is active */
Word16 *fac_ns, /* o : noise filling level, fac_ns_q */
Word16 *fac_ns_q /* o : quantized noise filling level, Q0 */
)
```
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issue