Increment breaking change no for doubly linked freelists (#44800)

Update breaking change number because doubly linked free lists use one additional bit in the method table pointer at the beginning of objects now.

Added a comment noting that gcDacVars->major_version_number that is set in gc.cpp is not actually checked by SOS, so SOS_BREAKING_CHANGE_VERSION should be updated if GC changes in a way that is incompatible with the existing SOS.

src/coreclr/src/gc/gc.cpp

@@ -40519,6 +40519,9 @@ void PopulateDacVars(GcDacVars *gcDacVars)
 #ifndef DACCESS_COMPILE
     assert(gcDacVars != nullptr);
     *gcDacVars = {};
+    // Note: these version numbers are not actually checked by SOS, so if you change
+    // the GC in a way that makes it incompatible with SOS, please change
+    // SOS_BREAKING_CHANGE_VERSION in both the runtime and the diagnostics repo
     gcDacVars->major_version_number = 1;
     gcDacVars->minor_version_number = 0;
     gcDacVars->built_with_svr = &g_built_with_svr_gc;

src/coreclr/src/inc/sospriv.idl

@@ -413,7 +413,7 @@ interface ISOSDacInterface8 : IUnknown
 // Increment anytime there is a change in the data structures that SOS depends on like
 // stress log structs (StressMsg, StressLogChunck, ThreadStressLog, etc), exception
 // stack traces (StackTraceElement), the PredefinedTlsSlots enums, etc.
-cpp_quote("#define SOS_BREAKING_CHANGE_VERSION 1")
+cpp_quote("#define SOS_BREAKING_CHANGE_VERSION 2")
 
 [
     object,

src/coreclr/src/pal/prebuilt/inc/sospriv.h

@@ -2675,7 +2675,7 @@ EXTERN_C const IID IID_ISOSDacInterface8;
 /* interface __MIDL_itf_sospriv_0000_0012 */
 /* [local] */ 
 
-#define SOS_BREAKING_CHANGE_VERSION 1
+#define SOS_BREAKING_CHANGE_VERSION 2
 
 
 extern RPC_IF_HANDLE __MIDL_itf_sospriv_0000_0012_v0_0_c_ifspec;