Include the following changes:
- Port custom MSBuild tasks to support "Enable granular control over app start/stop" (#10562) from v6.0
- Port custom MSBuild tasks to support "Rewrite IIS deployment functionality" (#10546) from v6.0
- Minor refactoring inside existing task implementations from v6.0
- Split IIS-related custom MSBuild tasks into separate DLL
This essentially syncs the code for the custom MSBuild task DLL's between v5.7 and v6.0. While v5.7 will not utilize the newly ported tasks, they'll be available for use in v5.7 by end-user custom code.