Inconsistent names were found using the following regular expressions.
* `rg "TEST(_F|_P)?\(\w+,\s+\w+Test\)"`
* `rg "TEST(_F|_P)?\(\w+,\s+Test\w+\)"`
* `rg "TEST(_F|_P)?\(\w+Tests,\s+\w+\)"`
Fixes#3495.
* Replace Matrix<> with Vector<> where vectors are explicitly intended.
I found these via `rg "Eigen::Matrix<double, \w+, 1>"`.
* Pass all Eigen matrices by const reference. I found these via `rg
"\(Eigen"` on main (the initializer list constructors make more false
positives).
* Replace MakeMatrix() and operator<< usage with initializer list
constructors. I found these via `rg MakeMatrix` and `rg "<<"`
respectively.
* Deprecate MakeMatrix()
There were three options for where to put this function:
1. A free function in LinearQuadraticRegulator.h. Returning a K matrix
means the user can't use the LinearQuadraticRegulator in a loop
anymore.
2. A default argument added to ctors in LinearQuadraticRegulator for a
time delay (default of 0). This has the smallest API footprint from
the user perspective, but it bloats the already substantial
constructor overload set of LinearQuadraticRegulator.
3. A member function in LinearQuadraticRegulator that modifies the
internal K. This would still have to take in a LinearSystem or (A, B)
pair because the ctor doesn't store it. Storing it internally feels
like paying for what we don't use most of the time.
I went with option 3.
I verified the tests's expected values in Python with
scipy.linalg.fractional_matrix_power().
Closes#2877.
