TextData Coverage and Minor Bug Fixes (#1744)

This had been intended to get 100% coverage for TextData functions, and it does that.
However, some minor bugs requiring source changes arose during testing.
- the Excel CHAR function restricts its argument to 1-255. PhpSpreadsheet CHARACTER
  had been allowing 0+. Also, there is no need to test if iconv exists,
  since it is part of Composer requirements.
- The DOLLAR function had been returning NUM for invalid arguments. Excel returns VALUE.
  Also, negative amounts were not being handled correctly.
- The FIXEDFORMAT function had been returning NUM for invalid arguments. Excel FIXED returns VALUE.

tests/data/Calculation/TextData/DOLLAR.php

@@ -6,11 +6,20 @@ return [
         123.456,
         2,
     ],
+    [
+        '$123.46',
+        123.456,
+    ],
     [
         '$123.32',
         123.321,
         2,
     ],
+    [
+        '($123.32)',
+        -123.321,
+        2,
+    ],
     [
         '$1,235,000',
         1234567,
@@ -22,12 +31,17 @@ return [
         -5,
     ],
     [
-        '#NUM!',
+        '($1,200,000)',
+        -1234567,
+        -5,
+    ],
+    [
+        '#VALUE!',
         'ABC',
         2,
     ],
     [
-        '#NUM!',
+        '#VALUE!',
         123.456,
         'ABC',
     ],