Adds compile operations to the CompilerDispatcherJob interface. As such,
introduces Compiler::PrepareUnoptimizedCompilationJob and updates the
unoptimized compilation path to use CompilationJobs. Also unifies
FinalizeCompilationJob to deal with both optimized and unoptimized
compilation jobs.

A dummy FullCodegenCompilationJob is also introduced, where all the work
is done in the ExecuteJob phase, which cannot be run on a
background thread.

BUG=v8:5203

Review-Url: https://codereview.chromium.org/2251713002
Cr-Commit-Position: refs/heads/master@{#38897}