Reference GDoc: Q3 Log modularity review [PROP3]

As described in the referenced GDoc: a cyclic dependency exists between src/os_layer and src/log modules.

The ideal is to transform the dependency to be either independent, or have unidirectional dependency. Alternatively reduction of the dependency in the form of fewer shared functions and data structures still represents a worthwhile improvement.

For this task os_layer is unclear. For os_posix there is a dependency on __wt_log_printf and WT_LOG_DSYNC. For os_win there is a dependency only on WT_LOG_DSYNC.