vfs/etc: Append std:: to size_t usages

Given we just recently had a patch backport this from citra, let's try
and keep the convention uniform.

src/core/file_sys/vfs.h

@@ -315,18 +315,19 @@ public:
     bool Rename(std::string_view name) override;
 };
 
-// Compare the two files, byte-for-byte, in increments specificed by block_size
-bool DeepEquals(const VirtualFile& file1, const VirtualFile& file2, size_t block_size = 0x1000);
+// Compare the two files, byte-for-byte, in increments specified by block_size
+bool DeepEquals(const VirtualFile& file1, const VirtualFile& file2,
+                std::size_t block_size = 0x1000);
 
 // A method that copies the raw data between two different implementations of VirtualFile. If you
 // are using the same implementation, it is probably better to use the Copy method in the parent
 // directory of src/dest.
-bool VfsRawCopy(const VirtualFile& src, const VirtualFile& dest, size_t block_size = 0x1000);
+bool VfsRawCopy(const VirtualFile& src, const VirtualFile& dest, std::size_t block_size = 0x1000);
 
 // A method that performs a similar function to VfsRawCopy above, but instead copies entire
 // directories. It suffers the same performance penalties as above and an implementation-specific
 // Copy should always be preferred.
-bool VfsRawCopyD(const VirtualDir& src, const VirtualDir& dest, size_t block_size = 0x1000);
+bool VfsRawCopyD(const VirtualDir& src, const VirtualDir& dest, std::size_t block_size = 0x1000);
 
 // Checks if the directory at path relative to rel exists. If it does, returns that. If it does not
 // it attempts to create it and returns the new dir or nullptr on failure.