Add Buffered BinaryReader to speed up Binlog reading

[yuehuang010]

WIP. Add Buffered BinaryReader to speed up Binlog reading. By directly buffering the stream, it can inline ReadByte() function into Read7BitEncodedInt(). Add BulkRead7BitEncodedInt() to read multiple numbers in one call.

[yuehuang010]

Perf comparison would be nice then

I ported these changes to a private BinLogViewer to open a 500mb binlog.

Before: Total opening time: 1:11.670, Loading: 51.482 s, Analyzing: 8.743 s, Indexing: 7.944 s, Allocated: 120,133,521,336 bytes, Nodes: 143,137,731, Strings: 3,903,327

After: Total opening time: 52.185 s, Loading: 31.396 s, Analyzing: 9.339 s, Indexing: 7.796 s, Allocated: 63,378,355,056 bytes, Nodes: 143,137,731, Strings: 3,903,327

Note: This removes the bottleneck and exposes other places for further optimize. The gains are much greater in unit testing than End to End.