AST: Source range of FuncDecl/ConstructorDecl should include the thrown type

When a function declaration has a body, its source range ends at the
closing curly brace, so it includes the `throws(E)`. However, a
protocol requirement doesn't have a body, and due to an oversight,
getSourceRange() was never updated to include the extra tokens
that appear after `throws` when the function declares a thrown
error type. As a result, unqualified lookup would fail to find a
generic parameter type, if that happened to be the thrown type.

Fixes rdar://problem/143950572.

tools/SourceKit/lib/SwiftLang/SwiftSourceDocInfo.cpp

@@ -890,17 +890,17 @@ static void setLocationInfo(const ValueDecl *VD,
 
   auto Loc = VD->getLoc(/*SerializedOK=*/true);
   if (Loc.isValid()) {
-    auto getSignatureRange =
+    auto getParameterListRange =
         [&](const ValueDecl *VD) -> std::optional<unsigned> {
       if (auto FD = dyn_cast<AbstractFunctionDecl>(VD)) {
-        SourceRange R = FD->getSignatureSourceRange();
+        SourceRange R = FD->getParameterListSourceRange();
         if (R.isValid())
           return getCharLength(SM, R);
       }
       return std::nullopt;
     };
     unsigned NameLen;
-    if (auto SigLen = getSignatureRange(VD)) {
+    if (auto SigLen = getParameterListRange(VD)) {
       NameLen = SigLen.value();
     } else if (VD->hasName()) {
       NameLen = VD->getBaseName().userFacingName().size();