AK: Add contains(char) method to String

AK/String.cpp

@@ -341,6 +341,11 @@ bool String::contains(const StringView& needle, CaseSensitivity case_sensitivity
     return StringUtils::contains(*this, needle, case_sensitivity);
 }
 
+bool String::contains(char needle, CaseSensitivity case_sensitivity) const
+{
+    return StringUtils::contains(*this, StringView(&needle, 1), case_sensitivity);
+}
+
 bool String::equals_ignoring_case(const StringView& other) const
 {
     return StringUtils::equals_ignoring_case(view(), other);

AK/String.h

@@ -138,6 +138,7 @@ public:
     [[nodiscard]] bool equals_ignoring_case(const StringView&) const;
 
     [[nodiscard]] bool contains(const StringView&, CaseSensitivity = CaseSensitivity::CaseSensitive) const;
+    [[nodiscard]] bool contains(char, CaseSensitivity = CaseSensitivity::CaseSensitive) const;
 
     [[nodiscard]] Vector<String> split_limit(char separator, size_t limit, bool keep_empty = false) const;
     [[nodiscard]] Vector<String> split(char separator, bool keep_empty = false) const;