Functionality to remove duplicate vertices and update
other vertex attributes and triangle indices is implemented.
The C++ and python tests are also written to test the code.

On branch sganjugu/remdup2
Changes to be committed:
modified:   cpp/open3d/t/geometry/TriangleMesh.cpp
modified:   cpp/open3d/t/geometry/TriangleMesh.h
modified:   cpp/pybind/t/geometry/trianglemesh.cpp
modified:   cpp/tests/t/geometry/TriangleMesh.cpp
modified:   python/test/t/geometry/test_trianglemesh.py

Previously, I was doing a manual copy and shrinking the vertices.
Instead in this checkin all vertex attributes, including the
coordinates are shrunk using IndexGet method using a vertex mask.

Further, the triangle index remapping is similar to what was done
earlier, with some simplications. One thing to note, is that
we cannot use utility::InclusivePrefixSum to remap vertex indices
because the duplicates can occur in any position and may be duplicates
of any earlier vertex.

For e.g., suppose there were 9 vertices to start with, and 8th (index 7, starting from 0),
was a duplicate of 2nd (index 1, starting from 0).

So, the vertex mask would look like this:
Vertex indices: [0, 1, 2, 3, 4, 5, 6, 7, 8]
Vertex mask:    [1, 1, 1, 1, 1, 1, 1, 0, 1]
Prefix sum:   [0, 1, 2, 3, 4, 5, 6, 7, 7, 8]
This gives an incorrect index map for 8th vertex, which is mapped to
index 7 instead of 1.

On branch sganjugu/remdup2
Your branch is up to date with 'origin/sganjugu/remdup2'.
Changes to be committed:
modified:   ../cpp/open3d/t/geometry/TriangleMesh.cpp
modified:   ../python/test/t/geometry/test_trianglemesh.py