[IR][NFC] Rename getBaseObject to getAliaseeObject

To better reflect the meaning of the now-disambiguated {GlobalValue,
GlobalAlias}::getBaseObject after breaking off GlobalIFunc::getResolverFunction
(D109792), the function is renamed to getAliaseeObject.

llvm/lib/Bitcode/Writer/BitcodeWriter.cpp

@@ -4039,7 +4039,7 @@ void ModuleBitcodeWriterBase::writePerModuleGlobalValueSummary() {
                                FSModVTableRefsAbbrev);
 
   for (const GlobalAlias &A : M.aliases()) {
-    auto *Aliasee = A.getBaseObject();
+    auto *Aliasee = A.getAliaseeObject();
     if (!Aliasee->hasName())
       // Nameless function don't have an entry in the summary, skip it.
       continue;