Add Array relational operator docs and FetchContent CMake guide

Pavel Guzenfeldrequested to merge
PavelGuzenfeld/eigen:docs/array-relational-ops-and-fetchcontent into master

Summary

Issue #2801 (closed) — Array relational operator documentation:

  • Add 6 relational operators (<, <=, >, >=, ==, !=) to the coefficient-wise math functions catalog in CoeffwiseMathFunctionsTable.dox
  • Each entry documents both array-array and array-scalar forms
  • Includes \warning for == / != about exact floating-point comparison

Issue #2793 (closed) — FetchContent CMake guide:

  • Add new FetchContent section to TopicCMakeGuide.dox
  • Documents FetchContent_Declare + FetchContent_MakeAvailable with EXCLUDE_FROM_ALL and GIT_SHALLOW
  • Documents disabling build options (EIGEN_BUILD_DOC, EIGEN_BUILD_TESTING, BUILD_TESTING, EIGEN_BUILD_PKGCONFIG) to avoid target collisions
  • Notes the CMake 3.30 CMP0168 behavioral change

Test plan

Documentation-only change (.dox files). No code modified.

Local Docker (GCC 15, CMake 3.31, Debian trixie, C++17):

Check Result
CMake configure ✅ configures OK
stl_iterators build + test ✅ pass (sanity check, no regressions)

Closes #2801 (closed) Closes #2793 (closed)

Edited by Pavel Guzenfeld

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