kernel: add some kernel dispatchers for matrix manipulation

[fingolfin]

Yet another commit from an unfinished branch/PR that might be considered useful on its own: faster "early methods" for SwapRows/SwapCols using kernel methods. It is not tested thoroughly and I am not even sure we want to go in this direction, but we could e.g. use this as basis for discussions during the GAP Days

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This speeds up swap operations for plain list matrices a lot, and even for "real" matrix objs, as the overhead of a GAP early method is much higher than the overhead of one written in the kernel.

Now whether this gain is worth the extra complexity is another question; though of course when doing heavy linear algebra, these row and column can add up.

Before:

gap> mat:=IdentityMat(10,Integers);;
gap> for i in [1..1000000] do SwapMatrixColumns(mat,1,2); od; time;
326
gap> for i in [1..1000000] do SwapMatrixRows(mat,1,2); od; time;
90
gap> for i in [1..1000000] do tmp:=mat[1];mat[1]:=mat[2];mat[2]:=tmp; od; time;
37

gap> mat:=IdentityMat(10,GF(2));; ConvertToMatrixRep(mat);; mat;
<a 10x10 matrix over GF2>
gap> for i in [1..1000000] do SwapMatrixRows(mat,1,2); od; time;
146
gap> for i in [1..1000000] do tmp:=mat[1];mat[1]:=mat[2];mat[2]:=tmp; od; time;
84

After:

gap> mat:=IdentityMat(10,Integers);;
gap> for i in [1..1000000] do SwapMatrixColumns(mat,1,2); od; time;
153
gap> for i in [1..1000000] do SwapMatrixRows(mat,1,2); od; time;
19
gap> for i in [1..1000000] do tmp:=mat[1];mat[1]:=mat[2];mat[2]:=tmp; od; time;
45

gap> mat:=IdentityMat(10,GF(2));; ConvertToMatrixRep(mat);; mat;
<a 10x10 matrix over GF2>
gap> for i in [1..1000000] do SwapMatrixRows(mat,1,2); od; time;
116
gap> for i in [1..1000000] do tmp:=mat[1];mat[1]:=mat[2];mat[2]:=tmp; od; time;
83