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/cpp-lexer.cpp

@@ -18,7 +18,7 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
     args_parser.parse(arguments);
 
     auto file = TRY(Core::Stream::File::open(path, Core::Stream::OpenMode::Read));
-    auto content = TRY(file->read_all());
+    auto content = TRY(file->read_until_eof());
     StringView content_view(content);
 
     Cpp::Lexer lexer(content);