Mutating variants of metric-related functions

[mateuszbaran]

@jlumpe pointed out on slack that we don't have mutating variants of metric-related functions and it sounds like a very good idea.

Functions:

• christoffel_symbols_first
• christoffel_symbols_second
• christoffel_symbols_second_jacobian
• einstein_tensor
• inverse_local_metric
• local_metric
• local_metric_jacobian
• ricci_tensor
• riemann_tensor (the basis variant)

[kellertuer]

Could we maybe collect a list of functions here? That might be helpful to resolve this.

[mateuszbaran]

Sure, I've listed them.