Faster Version of compute_cov_mtx_fx
# Basic info
<!--- Add commit SHA used to reproduce -->
# Bug description
compute_cov_mtx_fx Has heavy load in some profiles, running the encoder
# Ways to reproduce
e.g. producing a bitstream like shown below:
<!-- Commandline or script -->
```bash
IVAS_COD -mc 7_1_4 24400 48 stv71MC48c.wav stv71MC48c_24k4bps.wav
```
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task