Add CharacterLiteral support in trRValue

Character literals ('A', '\n', etc.) were falling through the rvalue
visitor's dyn_cast chain and producing 'unsupported rvalue expression
CharacterLiteral' diagnostics, which became (admit()) in the emitted
Pulse code.

Translate them as IntLit nodes of the appropriate (int) type, matching
how the C standard defines character constants. Verified on MSQuic's
src/core: eliminates all 286 CharacterLiteral diagnostics and reduces
the total admit count from 19,910 to 19,826 (-84).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: Copilot

cpp/impl.cpp

@@ -618,6 +618,11 @@ class PALConsumer : public ASTConsumer {
         return mk_int_lit(std::move(loc), toBigInt(il->getValue()),
                           std::move(ty));
       }
+    } else if (auto cl = dyn_cast<CharacterLiteral>(e)) {
+      auto ty = trQualType(cl->getType(), cl->getSourceRange());
+      return mk_int_lit(std::move(loc),
+                        mk_bigint(toStr(std::to_string(cl->getValue()))),
+                        std::move(ty));
     } else if (auto uo = dyn_cast<UnaryOperator>(e)) {
       switch (uo->getOpcode()) {
       case UO_AddrOf: