Add a note explaining the XXXX in the rule number to InternalsVisibleTo page

[BartoszKlonowski]

This pull request closes #44197.

Initially I aimed to make a note about necessity to replace CAXXXX with the proper CA's number that the page describes, but when writing that I noticed it makes the idea of having the generic page useless if we still need to provide non-generic NOTE for each page. At the same time I see the point of having that include a generic, so I didn't want to remove it totally and break DRY rule.

Eventually I went for extracting only the "non-generic" part, which is the code snippet, to avoid confusions and to still be able to include the part that is repeated for each CA using this IVT variable.

---

Internal previews

📄 File	🔗 Preview link
docs/fundamentals/code-analysis/quality-rules/ca1812.md	CA1812: Avoid uninstantiated internal classes
docs/fundamentals/code-analysis/quality-rules/ca1852.md	"CA1852: Seal internal types"

[gewarren]

@BartoszKlonowski I don't love this fix. For one thing, there is now a hanging colon at the end of the include file, so the include file can't stand "on its own". The second reason is that there are other include files that use this same pattern because they're shared between multiple CA rules, for example:

• docs/docs/fundamentals/code-analysis/includes/api-surface.md

  Line 6 in 3dfad5a

  dotnet_code_quality.CAXXXX.api_surface = private, internal

• docs/docs/fundamentals/code-analysis/includes/excluded-symbol-names.md

  Line 6 in 3dfad5a

  dotnet_code_quality.CAXXXX.excluded_symbol_names = MyType

• docs/docs/fundamentals/code-analysis/includes/excluded-type-names-with-derived-types.md

  Line 6 in 3dfad5a

  dotnet_code_quality.CAXXXX.excluded_type_names_with_derived_types = MyType

So we're breaking the pattern if we merge this PR. I think a better fix is to note, in the include file, that the "XXXX" should be replaced with the corresponding rule number.

[BartoszKlonowski]

Alright, putting the note in the include file didn't actually cross my mind, but I agree this is the good idea!

[BartoszKlonowski]

@gewarren Please let me know how you find the latest changes

[gewarren]

Thank you @BartoszKlonowski. I left a suggestion for slightly more succinct wording. Also, would you be able to add this note to the other shared include files that state CAXXXX? Thank you so much for your help with this.