replace docs links with source

This addresses another docs build warning. The docs build system flags absolute links to the pages on docs.microsoft.com as warnings, which should be replaced with relative links. This fix changes the link to the source doc on GitHub. I'm currently looking for a better solution.

proposals/csharp-7.2/private-protected.md

@@ -22,7 +22,7 @@ Directly providing support for this access level in C# enables these circumstanc
 
 ### `private protected` access modifier
 
-We propose to add a new access modifier combination `private protected` (which can appear in any order among the modifiers). This maps to the CLR notion of protectedAndInternal, and borrows the same syntax currently used in [C++/CLI](https://docs.microsoft.com/cpp/dotnet/how-to-define-and-consume-classes-and-structs-cpp-cli#BKMK_Member_visibility).
+We propose to add a new access modifier combination `private protected` (which can appear in any order among the modifiers). This maps to the CLR notion of protectedAndInternal, and borrows the same syntax currently used in [C++/CLI](https://github.com/MicrosoftDocs/cpp-docs/blob/master/docs/dotnet/how-to-define-and-consume-classes-and-structs-cpp-cli.md#-member-visibility).
 
 A member declared `private protected` can be accessed within a subclass of its container if that subclass is in the same assembly as the member.
 

proposals/csharp-7.3/blittable.md

@@ -120,7 +120,7 @@ There are a couple of alternatives to consider:
 The F# language encodes the constraint in the signature file which means C# cannot re-use their representation. A new attribute will need to be chosen for this constraint. Additionally a method which has this constraint must be protected by a mod-req.
 
 ### Blittable vs. Unmanaged
-The F# language has a very [similar feature](https://docs.microsoft.com/dotnet/articles/fsharp/language-reference/generics/constraints) which uses the keyword unmanaged. The blittable name comes from the use in Midori.  May want to look to precedence here and use unmanaged instead. 
+The F# language has a very [similar feature](https://github.com/dotnet/docs/blob/main/docs/fsharp/language-reference/generics/constraints.md) which uses the keyword unmanaged. The blittable name comes from the use in Midori.  May want to look to precedence here and use unmanaged instead. 
 
 **Resolution** The language decide to use unmanaged