Clarify breaking-change rules for properties

[mstefarov]

Would moving a public property up to a base class be considered a breaking change, in any sense?

The breaking-change-rules doc mentions that moving methods up is allowed. It seems like moving properties should be allowed too. But the Microsoft.DotNet.PackageValidation tool flags this as a breaking change.

And while we're at it, how about public events and indexers?

It would be good to get a definitive answer, and to have the doc and the validation tool in sync as well.

@jnm2 @stephentoub

[mstefarov]

Related: #29637
The doc previously said that moving members is allowed, but this was changed to methods after concerns were raised about moving public fields.

[jnm2]

It might also be good to mention nested types for clarity, since "members" of a type can include types. I would assume it's a breaking change to move a nested type to be nested in Base instead of Derived.

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[stephentoub]

It should be fine to move properties from a derived type to a base type.
cc: @bartonjs

[dotMorten]

In that case the package validation tools are broken