Add 3 new element-wise vector operations

[alexander-novo]

Description

Add a new vector operations:

• elementwiseDivide which performs like scale, but scales by the inverse of a diagonal matrix.
• elementwiseMax which computes a vector whose elements are the maximum of the corresponding elements in the two input vectors.
• abs which computes a vector whose elements are the absolute values of the corresponding element in the input vector.

Proposed changes

N/A

Checklist

• All tests pass (make test and make test_install per testing instructions). Code tested on
  • CPU backend
  • CUDA backend
  • HIP backend
• I have manually run the non-experimental examples and verified that residuals are close to machine precision. (In your build directory run:
  ./examples/<your_example>.exe -h to get instructions how to run examples). Code tested on:
  • CPU backend
  • CUDA backend
  • HIP backend
• Code compiles cleanly with flags -Wall -Wpedantic -Wconversion -Wextra.
• The new code follows Re::Solve style guidelines.
• There are unit tests for the new code.
• The new code is documented.
• The feature branch is rebased with respect to the target branch.
• I have updated CHANGELOG.md to reflect the changes in this PR. If this is a minor PR that is part of a larger fix already included in the file, state so.

Further comments

N/A

[pelesh]

I suggest we merge #408, then #411 before this PR.

@alexander-novo: #411 has some changes you may find helpful. Please rebase your branch to develop once #411 is merged.

CC @shakedregev

[alexander-novo]

Moved to #413