Rename fixed_base_scalar_mul.rs

[benesjan]

Problem

The file now contains not just fixed_base_scalar_mul function but also embedded_curve_add and variable_base_scalar_mul.

Rename the following 2 files:
acvm-repo/acvm/src/pwg/blackbox/fixed_base_scalar_mul.rs
acvm-repo/bn254_blackbox_solver/src/fixed_base_scalar_mul.rs

Happy Case

The file should be renamed to something more generic.

Project Impact

Nice-to-have

Impact Context

No response

Workaround

None

Workaround Description

No response

Additional Context

No response

Would you like to submit a PR for this Issue?

None

Support Needs

No response