[clang] [NFC][analyzer] Multipart checker refactor 1: VirtualCallChecker (PR #132072)

[Donát Nagy via cfe-commits]

================
@@ -42,8 +42,14 @@ namespace {
 class VirtualCallChecker
     : public Checker<check::BeginFunction, check::EndFunction, check::PreCall> {
 public:
-  // These are going to be null if the respective check is disabled.
-  mutable std::unique_ptr<BugType> BT_Pure, BT_Impure;
+  enum : CheckerPartIdx { PureChecker, ImpureChecker, NumCheckerParts };
+
+  BugType BugTypes[NumCheckerParts] = {
+      {this, PureChecker, "Pure virtual method call",
----------------
NagyDonat wrote:

By the way WDYT about changing `"Pure virtual method call"` to e.g.`"Call of pure virtual method"` (in a separate non-NFC follow-up commit)? When I first read this message, I parsed it as "(pure ((virtual method) call))" instead of the correct "(((pure virtual) method) call)" which confused me for 5-10 minutes.

https://github.com/llvm/llvm-project/pull/132072