Audit for proper "rule of 7" adherence in custom classes

[shinymerlyn]

Fayti1703 in Discord pointed out at least one example of a class that has this implemented wrong. In this case, it's writing to uninitialized data, but there are also other issues with this class:

overgrowth/Source/Graphics/font_renderer.cpp

Line 225 in 594a2a4

*impl_ = *other.impl_;

We should go through any custom class that has any of the "Big Seven" and either remove them when not needed, add the remaining "Big Seven" they're missing, or migrate all the lifetime management details to a class that only manages lifetime (smart pointers).

I use the count of "7" here in quotes, partly because this is a named idiom/problem in C++, and partly because it's also known as the rule of 3, 5, or 6, depending on which iteration of C++ it's talking about. And I am not 100% which C++ standard this codebase should be conforming to:

• https://www.club.cc.cmu.edu/~ajo/disseminate/C++Now2015.pdf
• https://en.cppreference.com/w/cpp/language/rule_of_three
• https://en.wikipedia.org/wiki/Rule_of_three_(C%2B%2B_programming)