AK: Move bijective-base-conversion into AK/String

This allows everybody to create a String version of their number
in a arbitrary bijective base. Bijective base meaning that the mapping
doesn't have a 0. In the usual mapping to the alphabet the follower
after 'Z' is 'AA'.
The mapping using the (uppercase) alphabet is used as a standard but
can be overridden specifying 'base' and 'map'.

The code was directly yanked from the Spreadsheet.

AK/String.h

@@ -93,6 +93,8 @@ public:
 
     [[nodiscard]] static String repeated(char, size_t count);
 
+    [[nodiscard]] static String bijective_base_from(size_t value, unsigned base = 26, StringView map = {});
+
     template<class SeparatorType, class CollectionType>
     [[nodiscard]] static String join(const SeparatorType& separator, const CollectionType& collection)
     {