[StaticAnalyzer] Use std::optional in BugReporter.cpp (NFC)

This is part of an effort to migrate from llvm::Optional to
std::optional:

https://discourse.llvm.org/t/deprecating-llvm-optional-x-hasvalue-getvalue-getvalueor/63716

clang/lib/StaticAnalyzer/Core/BugReporter.cpp

@@ -1569,8 +1569,8 @@ static void simplifySimpleBranches(PathPieces &pieces) {
 /// std::nullopt.
 ///
 /// Note that this does not do a precise user-visible character or column count.
-static Optional<size_t> getLengthOnSingleLine(const SourceManager &SM,
-                                              SourceRange Range) {
+static std::optional<size_t> getLengthOnSingleLine(const SourceManager &SM,
+                                                   SourceRange Range) {
   SourceRange ExpansionRange(SM.getExpansionLoc(Range.getBegin()),
                              SM.getExpansionRange(Range.getEnd()).getEnd());
 
@@ -1598,8 +1598,8 @@ static Optional<size_t> getLengthOnSingleLine(const SourceManager &SM,
 }
 
 /// \sa getLengthOnSingleLine(SourceManager, SourceRange)
-static Optional<size_t> getLengthOnSingleLine(const SourceManager &SM,
-                                              const Stmt *S) {
+static std::optional<size_t> getLengthOnSingleLine(const SourceManager &SM,
+                                                   const Stmt *S) {
   return getLengthOnSingleLine(SM, S->getSourceRange());
 }
 
@@ -1658,9 +1658,9 @@ static void removeContextCycles(PathPieces &Path, const SourceManager &SM) {
 
     if (s1Start && s2Start && s1Start == s2End && s2Start == s1End) {
       const size_t MAX_SHORT_LINE_LENGTH = 80;
-      Optional<size_t> s1Length = getLengthOnSingleLine(SM, s1Start);
+      std::optional<size_t> s1Length = getLengthOnSingleLine(SM, s1Start);
       if (s1Length && *s1Length <= MAX_SHORT_LINE_LENGTH) {
-        Optional<size_t> s2Length = getLengthOnSingleLine(SM, s2Start);
+        std::optional<size_t> s2Length = getLengthOnSingleLine(SM, s2Start);
         if (s2Length && *s2Length <= MAX_SHORT_LINE_LENGTH) {
           Path.erase(I);
           I = Path.erase(NextI);
@@ -1719,7 +1719,7 @@ static void removePunyEdges(PathPieces &path, const SourceManager &SM,
       std::swap(SecondLoc, FirstLoc);
 
     SourceRange EdgeRange(FirstLoc, SecondLoc);
-    Optional<size_t> ByteWidth = getLengthOnSingleLine(SM, EdgeRange);
+    std::optional<size_t> ByteWidth = getLengthOnSingleLine(SM, EdgeRange);
 
     // If the statements are on different lines, continue.
     if (!ByteWidth)