This rewrites the SysConf code for several reasons:
* Modernising the SysConf class. The naming was entirely cleaned up.
constexpr for constants.
* Exposing less stuff in the header.
* Probably less efficient parsing and writing logic, but much simpler
to understand and use in my opinion. No more hardcoded offsets.
No more duplicated code for the initial SYSCONF generation.
* More flexibility. It is now possible to add and remove entries,
since we rebuild the file. This allows us to stop spamming
"section not found" panic alerts; we can now use and insert
default entries.
Dolphin is able to generate one with all correct default settings, so
we don't need to ship with a pre-generated SYSCONF and worry about
syncing default settings.
Additionally, this commit changes SysConf to work with session SYSCONFs
so that Dolphin is able to generate a default one even for Movie/TAS.
Which SYSCONF needs to be touched is explicitly specified to avoid
confusion about which file SysConf is managing.
(Another notable change is that the Wii root functions are moved into
Core to prevent Common from depending on Core.)
