message: Readability: use absl::StrContains() instead of .find(..) != npos
diff: #include <set>
  #include <string>
  +#include "absl/strings/match.h"
  #include "absl/strings/str_cat.h"
  #include "absl/strings/string_view.h"
  #include "common/analysis/citation.h"
  @@ -69,7 +70,7 @@ void TokenStreamLintRule::HandleSymbol(const verible::Symbol& symbol,
  if (StringLiteralMatcher().Matches(symbol, &manager)) {
  const auto& string_node = SymbolCastToNode(symbol);
  const auto& string_literal = SymbolCastToLeaf(*string_node.children()[0]);
  - if (string_literal.get().text().find("\\\n") != std::string::npos) {
  + if (absl::StrContains(string_literal.get().text(), "\\\n")) {
  violations_.insert(LintViolation(symbol, kMessage, context));
  }
  }
  