Refactor and improve track establishment.

[B1ueber2y]

This file becomes quite short. Not sure if this needs to be a stand-alone file anymore. Can probably move to sth like global_mapper_impl.h/cc or just inline in global_mapper.h/cc.

The logic should be equivalent.

[B1ueber2y]

Regression:

I20260109 12:07:02.028296 1207130 compare.py:main:58] Results A - B:
=====scenes===== ======AUC @ X deg (%)====== ===images=== =components=
                  0.5    1.0    5.0    10.0     reg   all  num largest

==============================eth3d=dslr==============================
botanical_garden  -4.31  -1.74  -0.22  -0.10      0     0    0       0
boulders          -1.58  -0.82  -0.17  -0.08      0     0    0       0
bridge            -0.11  -0.06  -0.01  -0.01      0     0    0       0
courtyard         -5.30  -3.51  -0.67  -0.34      0     0    0       0
delivery_area      0.44   0.25   0.05   0.02      0     0    0       0
door               0.52   0.26   0.02   0.01      0     0    0       0
electro            7.09   8.30   6.25   4.67      0     0    0       0
exhibition_hall   -0.28  -0.06   0.02   0.11      0     0    0       0
facade            -0.26  -0.05  -0.00  -0.00      0     0    0       0
kicker             3.16   2.06   0.49   0.26      0     0    0       0
lecture_room      -0.02   0.05  -0.10  -0.05      0     0    0       0
living_room       -0.11  -0.08  -0.01  -0.00      0     0    0       0
lounge            -0.89  -0.45  -0.09  -0.04      0     0    0       0
meadow            -1.53  -1.94   6.24  12.64      0     0    0       0
observatory        0.20   0.17   0.05   0.03      0     0    0       0
office            -2.17  -3.95  -2.98  -2.03      0     0    0       0
old_computer       4.16   3.77   1.08   0.58      0     0    0       0
pipes              0.00   0.00   0.00   0.00      0     0    0       0
playground         0.64   0.34   0.07   0.04      0     0    0       0
relief             0.44   0.26   0.05   0.03      0     0    0       0
relief_2          -0.33  -0.17  -0.04  -0.02      0     0    0       0
statue            -0.06  -0.03  -0.01  -0.00      0     0    0       0
terrace            0.67   0.33   0.07   0.03      0     0    0       0
terrace_2          0.03  -0.05  -0.02  -0.01      0     0    0       0
terrains           2.06   1.69   0.39   0.22      0     0    0       0
----------------------------------------------------------------------
overall            0.36   0.48   0.33   0.28      0     0    0       0
----------------------------------------------------------------------
average            0.10   0.18   0.42   0.64      0     0    0       0