[Non-be][rend-non-be][split-non-be]SWB TBE: Fix constant in create_random_vector() to allow more reliable fixed point port.

• Related issues: #1465
• Requested reviewers: @multrus

Reason why this change is needed

• The refactoring allows a more reliable and bit exact output for the fixed point port, simply a division by 128 or right shift by 7.

Description of the change

• The constant "0.0078f" is changed to 0.0078125f, which is 1/128, which is the intended value for the index generation in create_random_vector().

Affected operating points

1. Produced bitstream is BE for EVS-MONO compared to previous state
2. Produced bitstream is non-BE for IVAS, but it is fully backwards compatible for decoding. Decoded output may differ.