Redo Calculation of Color Tinting (#3580)

* Redo Calculation of Color Tinting

Fix #3550. Some colors are specified in Excel by specifying a theme color to which a tint is applied. The original PHPExcel algorithm for doing this was developed by trial and error, and is good enough a lot of the time. However, for the issue at hand, the resulting color is detectably different from the calculation that Excel makes. Searching the web, I found https://gist.github.com/Mike-Honey/b36e651e9a7f1d2e1d60ce1c63b9b633 which comes much closer for the case in hand, and for all the other cases that I've looked at. That code depends on Python colorsys package; I have adapted the code from the Python gist and package into a new Php class. This doesn't agree perfectly with Excel. However, if each of the red, green, and blue components (each a value between 0 and 255 inclusive) agree within plus or minus 3 (arbitrary choice) of Excel's result, I think that is good enough.

I have added a new test member which reads from a spreadsheet with Xml altered by hand to set up several theme/tint cells. These tests use the plus-or-minus-3 criterion. They result in 100% code coverage of the new class.

Unsuprisingly, some existing tests failed with the new code. Issue2387Test reads a theme/tint font color, and is changed to use the plus-or-minus-3 criterion, comparing against the color as Excel shows it.

ColorChangeBrightness showed 9 failures with the new code. It consists of calculations not involving a spreadsheet. For that reason, I felt it was sufficient to just do an exact match test, changing the 9 old results for new results confirmed with the Python code. I also added one new test case, the one that kicked off this entire PR.

* Scrutinizer Being Stupid

It strikes again.

tests/data/Style/Color/ColorChangeBrightness.php

@@ -9,7 +9,7 @@ return [
     ],
     // RGBA
     [
-        'FF99A8B7',
+        'FF92A8BE',
         'FFAABBCC',
         -0.1,
     ],
@@ -20,17 +20,17 @@ return [
         0.1,
     ],
     [
-        '99A8B7',
+        '92A8BE',
         'AABBCC',
         -0.1,
     ],
     [
-        'FF1919',
+        'FF1A1A',
         'FF0000',
         0.1,
     ],
     [
-        'E50000',
+        'E60000',
         'FF0000',
         -0.1,
     ],
@@ -40,7 +40,7 @@ return [
         0.1,
     ],
     [
-        'E57373',
+        'FF5959',
         'FF8080',
         -0.1,
     ],
@@ -50,7 +50,7 @@ return [
         0.15,
     ],
     [
-        'D80000',
+        'D90000',
         'FF0000',
         -0.15,
     ],
@@ -60,18 +60,23 @@ return [
         0.15,
     ],
     [
-        'D86C6C',
+        'FF4646',
         'FF8080',
         -0.15,
     ],
     [
-        'FFF783',
+        'FFF984',
         'FFF008',
         0.5,
     ],
     [
-        '7F7804',
+        '847D00',
         'FFF008',
         -0.5,
     ],
+    'issue 3550' => [
+        '558ED5',
+        '1F497D',
+        0.39997558519241921,
+    ],
 ];