[AST] NFC: Capitalize UsingSpecifier::nonisolated for consistency

(cherry picked from commit 21ec592)

Author: xedin

include/swift/AST/Decl.h

@@ -270,17 +270,13 @@ static_assert(uint8_t(SelfAccessKind::LastSelfAccessKind) <
 
 enum class UsingSpecifier : uint8_t {
   MainActor,
-  nonisolated,
-  LastSpecifier = nonisolated,
+  Nonisolated,
+  LastSpecifier = Nonisolated,
 };
 enum : unsigned {
   NumUsingSpecifierBits =
       countBitsUsed(static_cast<unsigned>(UsingSpecifier::LastSpecifier))
 };
-static_assert(uint8_t(UsingSpecifier::LastSpecifier) <
-                  (NumUsingSpecifierBits << 1),
-              "UsingSpecifier is too small to fit in UsingDecl specifier bits. "
-              "Please expand ");
 
 /// Diagnostic printing of \c SelfAccessKind.
 llvm::raw_ostream &operator<<(llvm::raw_ostream &OS, SelfAccessKind SAK);

lib/AST/Decl.cpp

@@ -1850,7 +1850,7 @@ std::string UsingDecl::getSpecifierName() const {
   switch (getSpecifier()) {
   case UsingSpecifier::MainActor:
     return "@MainActor";
-  case UsingSpecifier::nonisolated:
+  case UsingSpecifier::Nonisolated:
     return "nonisolated";
   }
 }

lib/IDE/CompletionLookup.cpp

@@ -397,7 +397,7 @@ void CompletionLookup::addUsingSpecifiers() {
     case UsingSpecifier::MainActor:
       Builder.addTextChunk("@MainActor");
       break;
-    case UsingSpecifier::nonisolated:
+    case UsingSpecifier::Nonisolated:
       Builder.addTextChunk("nonisolated");
       break;
     }

lib/Parse/ParseDecl.cpp

@@ -6676,7 +6676,7 @@ ParserResult<UsingDecl> Parser::parseDeclUsing(ParseDeclOptions Flags,
   std::optional<UsingSpecifier> Specifier =
       llvm::StringSwitch<std::optional<UsingSpecifier>>(RawSpecifier.str())
           .Case("MainActor", UsingSpecifier::MainActor)
-          .Case("nonisolated", UsingSpecifier::nonisolated)
+          .Case("nonisolated", UsingSpecifier::Nonisolated)
           .Default(std::nullopt);
 
   if (!Specifier) {

lib/Sema/TypeCheckConcurrency.cpp

@@ -6495,7 +6495,7 @@ DefaultIsolationInSourceFileRequest::evaluate(Evaluator &evaluator,
     case UsingSpecifier::MainActor:
       setIsolation(D, DefaultIsolation::MainActor);
       break;
-    case UsingSpecifier::nonisolated:
+    case UsingSpecifier::Nonisolated:
       setIsolation(D, DefaultIsolation::Nonisolated);
       break;
     }