Add more analyzer coverage for coding style guidelines

[JeremyKuhne]

Not all of our coding style guidelines are covered by analyzers. https://github.com/dotnet/winforms/blob/main/docs/coding-style.md Some things that currently aren't covered:

• XML comments indented by a space
• Line breaks start with operators: || at the beginning of the line for example
• => stays on the previous line (for better alignment of further line breaks)
• t_ for thread statics
• unsafe on methods or classes only
• No empty XML comment blocks
• = can be aligned in some cases
• ?: should be on a single line or broken starting two lines with ? and :

[JeremyKuhne]

@sharwell here is the tracking issue from our off-line discussion

[sharwell]

XML comments indented by a space

Does not currently exist, but can be implemented based on SA1004 (Documentation lines should begin with a single space).

Line breaks start with operators: || at the beginning of the line for example ?: should be on a single line or broken starting two lines with ? and :

Related to https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/748.

=> stays on the previous line (for better alignment of further line breaks) t_ for thread statics unsafe on methods or classes only = can be aligned in some cases

I'm not aware of these already existing.

No empty XML comment blocks

Already implemented as SA1627 (Documentation text should not be empty).