clang-format: [JS] Treat regex literals like string literals.

Using the token type "unknown" can interfere badly with
WhitespaceManager's way of handling multiline comments.

llvm-svn: 241273
diff --git a/clang/lib/Format/Format.cpp b/clang/lib/Format/Format.cpp
index f97e1fb..2bbe4c63 100644
--- a/clang/lib/Format/Format.cpp
+++ b/clang/lib/Format/Format.cpp
@@ -808,6 +808,8 @@
         Tokens.resize(Tokens.size() - TokenCount);
         Tokens.back()->Tok.setKind(tok::unknown);
         Tokens.back()->Type = TT_RegexLiteral;
+        // Treat regex literals like other string_literals.
+        Tokens.back()->Tok.setKind(tok::string_literal);
         Tokens.back()->ColumnWidth += LastColumn - I[0]->OriginalColumn;
         return true;
       }