Two MPL optimization on Property evaluations

See individual commits for changes => review commit-wise.

Some measurements to master. Improvement is (1 - master/this MR).

Phase transition unit test; improvement 31%

bin/testrunner --gtest_filter=ProcessLib.TH2MPhaseTransition --gtest_repeat=1
master:  11.31s user 0.03s system 99% cpu 11.352 total
this MR: 7.74s user 0.02s system 99% cpu 7.777 total

TH2M heat pipe; improvement 17%

time bin/ogs ../s/Tests/Data/TH2M/TH2/heatpipe/heat_pipe_strict.prj > /dev/null
master:  31.38s user 0.15s system 99% cpu 31.569 total
this MR: 25.74s user 0.09s system 99% cpu 25.856 total

TRM point heat source; improvement 5%

time bin/ogs ../s/Tests/Data/ThermoRichardsMechanics/PointHeatSource/point_heat_source_2D.prj >/dev/null
master:  4.18s user 0.14s system 99% cpu 4.333 total
this MR: 3.96s user 0.12s system 99% cpu 4.087 total

HM; no improvement.

time bin/ogs ../s/Tests/Data/HydroMechanics/Verification/hm2_2Dmandel.prj >/dev/null
master:  503.99s user 44.54s system 611% cpu 1:29.76 total
this MR: 503.33s user 44.98s system 611% cpu 1:29.61 total

1. Feature description was added to the changelog
2. Tests covering your feature were added? Existing tests
3. Any new feature or behaviour change was documented?