Fix race condition when updating sources

The current implementation has a potential race condition under the following scenario:

Task updater              Driver

                          acquire lock
                          process new sources
                          ...
                          process new sources in lock release code
add new source
fail to acquire lock
 (sources not processed)
                          release lock

This results in new sources not being processed and the query getting stuck
if the task updater never call update sources again and the driver becomes
blocked because data from all current exchanges are consumed
Remove unused methods on Page
Convert Page size to be a long in bytes

Simplify OperatorContext stats
Remove Page dependencies on Guava
Remove Page.getSingleValueBlocks(position)
Move Page to SPI
Remove PageBuilder dependencies on Guava
Move PageBuilder to SPI
Add ConnectorPageSource to SPI

Move ConnectorDataStreamProvider to SPI and rename to ConnectorPageSourceProvider
Simplify InformationSchemaPageSourceProvider using a FixedPageSource
Replace AlignmentOperator with RaptorPageSource
Merge InternalConnector into Connector