This lets users continue using runtime-sideeffect Decorators if they choose,
only down-leveling the marked ones to Annotations.
Also remove the "skipTemplateCodegen" option, which is no longer needed
since Angular compiles with tsc-wrapped rather than ngc. The former doesn't
include any codegen.
This reverts commit c3fafa0651afd07b6fb5905b426121b2467e16c3.
The symbols should be configured at the component level and not be global to the compiler.