Resurrected the option to suppress in source using attributes (see https://github.com/dotnet/roslyn/issues/17218)
The code was taken from the history (https://github.com/dotnet/roslyn/tree/4dfefe7b49c33d1d078494d52a84b16772158b11) and adapted to latest changes.
TODO:
* add unit tests
* title needs translation

* Move Roslyn to newer toolset packages

1. Move to 1.2.1 compiler toolset package.
2. Move to 1.2.0-beta1 analyzer packages.
3. Turn on IOperation feature flag for all projects as the new analyzer packages have IOperation based analyzers.

* Use the Roslyn wide default CA rulesets for newly added samples project.

* Fix couple of test projects to use the Roslyn wide rulesets for code analysis.

* Move to analyzers 1.2.0-beta2 packages (multiple fixes and enhancements to Roslyn diagnostic analyzers)

* Revert accidental file mode changes.

* Move shipped implicit constructors to public API shipped files.

Fixes #11446

1. "Suppress active issues" command from solution explorer was doing couple of builds - one command line build to compute the FxCop diagnostics and another intellisense build to fetch Roslyn diagnostics. This change removes the second build and instead uses the diagnostics emitted from the build for suppression.

2. Bulk suppressing multiple diagnostics from error list/suppress active issues command was spending more than 50% of time in formatting the generated global suppressions file. This delay grows significantly larger with 1000+ issues being suppressed. This fix changes us to not format the entire suppressions file at once, but instead format each attribute separately and avoid formatting the batched file. This significantly brings down the formatting time.

3. Thread in the cancellation token during batch fix computation - otherwise cancelling the wait dialog while computing suppressions fix will make VS unresponsive.

Fixes #6066

1. "Suppress active issues" command from solution explorer was doing couple of builds - one command line build to compute the FxCop diagnostics and another intellisense build to fetch Roslyn diagnostics. This change removes the second build and instead uses the diagnostics emitted from the build for suppression.

2. Bulk suppressing multiple diagnostics from error list/suppress active issues command was spending more than 50% of time in formatting the generated global suppressions file. This delay grows significantly larger with 1000+ issues being suppressed. This fix changes us to not format the entire suppressions file at once, but instead format each attribute separately and avoid formatting the batched file. This significantly brings down the formatting time.

3. Thread in the cancellation token during batch fix computation - otherwise cancelling the wait dialog while computing suppressions fix will make VS unresponsive.

Fixes #6066