Spreadsheet: Use String::bijective_base_from for column name resolution

Updated Spreadsheet to use the new way of converting a number to a
String represenation using the alphabet.
The code responsible for this conversion now lives in AK/String, so it
gets deleted from Spreadsheet.cpp.

Userland/Applications/Spreadsheet/Spreadsheet.cpp

@@ -82,33 +82,6 @@ size_t Sheet::add_row()
     return m_rows++;
 }
 
-static String convert_to_string(size_t value, unsigned base = 26, StringView map = {})
-{
-    if (map.is_null())
-        map = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
-
-    VERIFY(base >= 2 && base <= map.length());
-
-    // The '8 bits per byte' assumption may need to go?
-    Array<char, round_up_to_power_of_two(sizeof(size_t) * 8 + 1, 2)> buffer;
-    size_t i = 0;
-    do {
-        buffer[i++] = map[value % base];
-        value /= base;
-    } while (value > 0);
-
-    // NOTE: Weird as this may seem, the thing that comes after 'Z' is 'AA', which as a number would be '00'
-    //       to make this work, only the most significant digit has to be in a range of (1..25) as opposed to (0..25),
-    //       but only if it's not the only digit in the string.
-    if (i > 1)
-        --buffer[i - 1];
-
-    for (size_t j = 0; j < i / 2; ++j)
-        swap(buffer[j], buffer[i - j - 1]);
-
-    return String { ReadonlyBytes(buffer.data(), i) };
-}
-
 static size_t convert_from_string(StringView str, unsigned base = 26, StringView map = {})
 {
     if (map.is_null())
@@ -119,7 +92,7 @@ static size_t convert_from_string(StringView str, unsigned base = 26, StringView
     size_t value = 0;
     for (size_t i = str.length(); i > 0; --i) {
         auto digit_value = map.find_first_of(str[i - 1]).value_or(0);
-        // NOTE: Refer to the note in `convert_to_string()'.
+        // NOTE: Refer to the note in `String::bijective_base_from()'.
         if (i == str.length() && str.length() > 1)
             ++digit_value;
         value = value * base + digit_value;
@@ -130,7 +103,7 @@ static size_t convert_from_string(StringView str, unsigned base = 26, StringView
 
 String Sheet::add_column()
 {
-    auto next_column = convert_to_string(m_columns.size());
+    auto next_column = String::bijective_base_from(m_columns.size());
     m_columns.append(next_column);
     return next_column;
 }
@@ -491,11 +464,11 @@ Position Sheet::written_data_bounds() const
 
 /// The sheet is allowed to have nonstandard column names
 /// this checks whether all existing columns are 'standard'
-/// (i.e. as generated by 'convert_to_string()'
+/// (i.e. as generated by 'String::bijective_base_from()'
 bool Sheet::columns_are_standard() const
 {
     for (size_t i = 0; i < m_columns.size(); ++i) {
-        if (m_columns[i] != convert_to_string(i))
+        if (m_columns[i] != String::bijective_base_from(i))
             return false;
     }
 
@@ -626,7 +599,7 @@ RefPtr<Sheet> Sheet::from_xsv(const Reader::XSV& xsv, Workbook& workbook)
     } else {
         sheet->m_columns.ensure_capacity(cols.size());
         for (size_t i = 0; i < cols.size(); ++i)
-            sheet->m_columns.append(convert_to_string(i));
+            sheet->m_columns.append(String::bijective_base_from(i));
     }
     for (size_t i = 0; i < max(rows, Sheet::default_row_count); ++i)
         sheet->add_row();