Add some custom keypad letter mappings

See FossifyOrg/Phone#139

commons/src/main/kotlin/org/fossify/commons/extensions/String.kt

@@ -290,7 +290,7 @@ fun String.formatPhoneNumber(minimumLength: Int = 4): String {
 
 fun String.highlightTextFromNumbers(textToHighlight: String, primaryColor: Int): SpannableString {
     val spannableString = SpannableString(this)
-    val digits = PhoneNumberUtils.convertKeypadLettersToDigits(this)
+    val digits = KeypadHelper.convertKeypadLettersToDigits(this)
     if (digits.contains(textToHighlight)) {
         val startIndex = digits.indexOf(textToHighlight, 0, true)
         val endIndex = Math.min(startIndex + textToHighlight.length, length)

commons/src/main/kotlin/org/fossify/commons/helpers/KeypadHelper.kt

@@ -0,0 +1,38 @@
+package org.fossify.commons.helpers
+
+import android.telephony.PhoneNumberUtils
+
+/**
+ * Mostly depends on [android.telephony.PhoneNumberUtils].
+ */
+object KeypadHelper {
+    // this should probably be split into language-specific mappings
+    private val KEYPAD_MAP = mutableMapOf<Char, Int>().apply {
+        put('ı', 4)
+        put('İ', 4)
+
+        put('ł', 5)
+        put('Ł', 5)
+    }
+
+    /**
+     * Translates any alphabetic letters (i.e. [A-Za-z]) in the
+     * specified phone number into the equivalent numeric digits,
+     * according to the phone keypad letter mapping described in
+     * ITU E.161 and ISO/IEC 9995-8.
+     *
+     * @return the input string, with alpha letters converted to numeric
+     * digits using the phone keypad letter mapping. For example,
+     * an input of "1-800-FOSS-411" will return "1-800-3667-411".
+     */
+    fun convertKeypadLettersToDigits(input: String): String {
+        val digits = PhoneNumberUtils.convertKeypadLettersToDigits(input)
+        val result = StringBuilder(digits.length)
+        for (c in digits) {
+            val digit = KEYPAD_MAP[c] ?: c
+            result.append(digit)
+        }
+
+        return result.toString()
+    }
+}