LibCore: Rename Stream::read_all to read_until_eof

This generally seems like a better name, especially if we somehow also
need a better name for "read the entire buffer, but not the entire file"
somewhere down the line.

Userland/Utilities/test-fuzz.cpp

@@ -152,7 +152,7 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
     auto fn = parse_target_name(type);
 
     auto file = TRY(Core::Stream::File::open(filename, Core::Stream::OpenMode::Read));
-    auto input = TRY(file->read_all());
+    auto input = TRY(file->read_until_eof());
 
     return fn(input.data(), input.size());
 }