Optimization of initialization phase

[sframba]

This PR includes a few optimizations by @jiemeng-total and @acitrain on the initialization phase of GEOSX, especially for mesh levels higher than zero.

Specifically:

• a few variable declarations were taken out of loops;
• in the MeshLevel constructor, costly repeated resizing is now avoided.

Edit: Here are two output from Caliper showing you the impact of Jie's modification on an high order case, the initialization time is nearly divided by 60 (the run time optimization is the result of PR 2123, not yet merged)

Without modification:

With the modification: