Remove mjData.qLDiagSqrtInv, add corresponding argument to mj_solveM2.

- `qLDiagSqrtInv` is only required for the dual solvers. It is now computed as-needed rather than unconditionally.
- `mj_solveM2` now requires a new input array `sqrtInvD` which contains the square root of the inverse diagonal D (formerly saved in `qLDiagSqrtInv`).

PiperOrigin-RevId: 710805133
Change-Id: I0622d6a8da3882916824e9c10bad9223c122c321

introspect/structs.py

@@ -5213,14 +5213,6 @@ STRUCTS: Mapping[str, StructDecl] = dict([
                  doc='1/diag(D)',
                  array_extent=('nv',),
              ),
-             StructFieldDecl(
-                 name='qLDiagSqrtInv',
-                 type=PointerType(
-                     inner_type=ValueType(name='mjtNum'),
-                 ),
-                 doc='1/sqrt(diag(D))',
-                 array_extent=('nv',),
-             ),
              StructFieldDecl(
                  name='bvh_aabb_dyn',
                  type=PointerType(