refactor: rename ScalarMultiplication -> ScalarMul

[yelhousni]

Rename ScalarMultiplication() to ScalarMul(). Needs Consensys/gnark-crypto#220 PR to be merged first.

[yelhousni]

In Groth16 the prover computes 3 ScalarMul() with random scalars r and s (2 G1, 1 G2). These call the internal mulGLV() which first split the random r and s into sub-scalars before hitting the for loop. I tried to remove the SplitScalar() from the mulGLV() and put it explicitly in ScalarMul(). This way one can sample directly random sub-scalars and use MulGLV() instead of ScalarMul(). However it's just a -1% after PR Consensys/gnark-crypto#213 which speeds up the scalar decomposition.

[gbotrel]

Let's discuss here: Consensys/gnark-crypto#224

[yelhousni]

closing this after Consensys/gnark-crypto#224