Show primitive mapping in the Mesh Boolean examples

[Fedr]

Nothing in the examples demonstrated BooleanResultMapper — the way to relate faces, vertices and edges of the input meshes to the primitives of the boolean result.

All five language variants (C++, C, Python, C#, JavaScript) now pass a mapper to the operation and use it to report:

• the faces of the result produced by each input mesh, and the faces the cut itself created (map over the inputs' valid faces, newFaces);
• one particular face of the first input mesh mapped forward to the faces of the result it produced — the cut can split one input face into several, or drop it entirely;
• a face of the result mapped back to the input face it came from, via getNew2OldFaceMap.

For the two spheres in the examples that prints:

faces from sphere1: 2670
faces from sphere2: 2670
faces created by the cut: 1344
face 793 of sphere1 produced 4 faces of the result: 8542 8543 8544 8545
face 8542 of the result came from face 793 of sphere1

Fix in getNew2OldFaceMap

Writing the reverse example surfaced an off-by-one: the map was sized maxNewFace (the largest new face id) rather than maxNewFace + 1, so outMap[nf] = of for that largest id wrote one element past the end of the vector — an assert in a Debug build, an out-of-bounds write in Release — and the returned map never contained the entry for the last mapped face. For the spheres above, the last face of the result coming from A is 8863 while the map's size was 8863; it is now 8864 and that face resolves to its origin, 7199.

No test asserted on the size of the returned map, so nothing else changes.

Docs

• doxygen/examples/MeshBoolean.dox mentions the mapper and the reverse map above the tabs.
• MR::BooleanResultMapper's doc comment now shows the two new C++ snippets (markers 1 and 2), the same way MR::boolean shows marker 0.

Verification

• The C++ example compiles and links against a locally built MRMesh (with the fix) and prints the output above; the reverse lookup of the last A face was checked separately against both the old and the new sizing.
• The Python example prints the same numbers with the installed meshlib wheel.
• The C example compiles clean (cl /W3) against the generated MeshLibC2 headers.
• The C# and JS variants mirror API usage already covered by MRDotNet2Test/src/BooleanTests.cs, MRWasmTest/booleanMapper.test.mjs and the neighbouring examples (FaceBitSet.fromIndices, FaceMap.toArray, the using disposal style).

CI: ubuntu-x64 (C++ and C examples, MRTest) and windows (C# examples) are enabled; the other platforms are disabled.