Migrates a remaining common file over to the Common namespace, making it
consistent with the rest of common files.
This also allows for high-traffic FS related code to alias the
filesystem function namespace as
namespace FS = Common::FS;
for more concise typing.
The deep recursion has caused issues in certain games with large numbers of files, especially with MSVC builds.
Previously the recursion depth is about equal to the number of files present. With this the depth should be about equal to the maximum depth of the directory structure of the RomFS.
This implementation is different from Luma3DS's which directly hooks the SDK functions. Instead, we read the RomFS's metadata and figure out the directory and file structure. Then, relocations (i.e. replacements/deletions/patches) are applied. Afterwards, we rebuild the metadata, and assign 'fake' data offsets to the files. When we want to read file data from this rebuilt RomFS, we use binary search to find the last data offset smaller or equal to the given offset and read from that file (either from the original RomFS, or from replacement files, or from buffered data with patches applied) and any later files when length is not enough.
The code that rebuilds the metadata is pretty complex and uses quite a few variables to keep track of necessary information like metadata offsets. According to my tests, it is able to build RomFS-es identical to the original (but without trailing garbage data) when no relocations are applied.
