Disable SA1412 by default until we can work out the usability problems

[sharwell]

SA1412 "works", but it currently has several usability problems that people need to be aware of before applying it to their projects. We should set the diagnostic as DisabledByDefault until we figure out how to address the other issues.

Current issues related to this:

• SA1412 code fix does not work properly on linked files #1168
• SA1412 "fix all" does not work properly on files that are closed #1169
• SA1412 code fix does not preserve DependentUpon solution items #1239

[Noryoko]

Grabbing.

[julealgon]

@sharwell , I found this issue because I intended to ask a question regarding why this specific analyzer rule was turned off by default. While I'm glad I found it and thus won't need to create my question issue, I'd propose that the reason why the rule has been disabled by default be made explicit in the documentation page for the rule, or at least in the dotnetanalyzers.github.io page.

All it says there today is this:

📝 This rule is new for StyleCop Analyzers, and was not present in StyleCop Classic.

I believe exposing the reason as to why it is disabled by default would help other folks looking for the information like I was.

This of course goes for any other "disabled-by-default" rule.