[clangd] Re-enable clang-tidy's nolint blocks

[hokein]

Summary

The previous inefficient implementation is polished.

[kadircet]

thanks, sorry for missing this!

clang-tools-extra/clangd/ParsedAST.cpp

ASTDiags.setLevelAdjuster([&](DiagnosticsEngine::Level DiagLevel,
           // to match clang-tidy's behaviour.
           bool IsInsideMainFile =
               Info.hasSourceManager() &&
               isInsideMainFile(Info.getLocation(), Info.getSourceManager());
           SmallVector<tooling::Diagnostic, 1> TidySuppressedErrors;
           if (IsInsideMainFile && CTContext->shouldSuppressDiagnostic(
                                       DiagLevel, Info, TidySuppressedErrors,
                                       /*AllowIO=*/false,
-                                      /*EnableNolintBlocks=*/false)) {
+                                      /*EnableNolintBlocks=*/true)) {
             // FIXME: should we expose the suppression error (invalid use of
             // NOLINT comments)?
             return DiagnosticsEngine::Ignored;
           }
 
           // Check for warning-as-error.
           if (DiagLevel == DiagnosticsEngine::Warning &&
               CTContext->treatAsError(CheckName)) {

clang-tools-extra/clangd/unittests/DiagnosticsTests.cpp

int main() {
       // NOLINTNEXTLINE
       double e = 8 / i;
       #define BAD 8 / i
       double f = BAD;  // NOLINT
       double g = [[8]] / i;
       #define BAD2 BAD
       double h = BAD2;  // NOLINT
       // NOLINTBEGIN
-      // FIXME: re-enable when NOLINTBEGIN suppresss block is enabled in clangd.
-      // double x = BAD2;
-      // double y = BAD2;
+      double x = BAD2;
+      double y = BAD2;
       // NOLINTEND
 
       // verify no crashes on unmatched nolints.
       // NOLINTBEGIN
     }
   )cpp");
   TestTU TU = TestTU::withCode(Main.code());
   TU.ClangTidyProvider = addTidyChecks("bugprone-integer-division");