* Add Ability to Ignore Cell Errors in Excel
Fix#1141, which had been closed as stale, but which I have reopened. Excel will show cells with certain "errors" with a green triangle in the upper left. The suggestion in the issue to use quotePrefix to suppress the numberStoredAsText error is ineffective. In Excel, the user can turn this indicator off for individual cells. Cells where this is turned off can be detected at read time, and PhpSpreadsheet will now process those. In addition, the user can explicitly set the ignored error as in Excel.
```php
$cell->setIgnoredErrorNumberStoredAsText(true);
```
There are a number of different errors that can be ignored in this fashion. This PR implements `numberStoredAsText` (which is likely to be by far the most useful one), `formula`, `twoDigitTextYear`, and `evalError`, all of which are demonstrated in the new test spreadsheet. There are several others for which I am not able to create good examples; I have not implemented those, but they can be easily added if needed (`calculatedColumn`, `emptyCellReference`, `formulaRange`, `listDataValidation`, and `unlockedFormula`).
* Scrutinizer
A new change, a new Scrutinizer false positive.
* Move Ignored Errors to Own Class
In response to comments from @MarkBaker, implement ignoredError as a new class. This simplifies Cell by requiring only 1 new method, rather than 8+. This requires a slightly more complicated syntax.
```php
$cell->getIgnoredErrors()->setNumberScoredAsText(true);
```
Mark had also suggested that there might be a pre-existing regexp for processing the cells/cellranges when reading the sqref attribute. Those in Calculation are too complicated (read "non-performant") for this piece of code; the one in Coordinates is slightly less complicated than Calculation, but still more complicated than the one I'm using, and doesn't handle ranges.
Fix#3495. This seems to be a bug in Excel, one which it manages to cover up but PhpSpreadsheet is affected. User enters a formula preceded by an apostrophe into a cell. Excel turns on `quotePrefix` style and stores the data as a string rather than a formula. User now enters a formula not preceded by an apostrophe into the same cell. Excel stores it is a formula but does not turn `quotePrefix` off. When the spreadsheet is saved, the cell's style specifies `quotePrefix`, but the cell's content indicates it's a formula. Till now, PhpSpreadsheet sees that quotePrefix is set, and therefore treats the cell's contents as a string rather than a formula. This PR will change that behavior so that quotePrefix is automatically turned off when Xlsx Reader sees that the cell indicates that it is a formula.
* Font Themes
It isn't a feature of Excel that I've made any use of, but PR #3476 added better Theme support for colors, and it is relatively easy to add Theme support for Fonts on top of that.
Excel assigns two theme fonts to its spreadsheets, one for Headings (major), and one for Body (minor). If the body theme is Calibri, when you choose a font for a cell in Excel, you can choose 'Calibri (Body)' from the Theme Fonts section at the top of the Font dropdown, or 'Calibri' from the 'All Fonts' section. If you choose the former, the cell will be automatically restyled if you change the Theme Fonts (via Page Layout, Themes, Fonts). The relationship to the theme fonts is recorded in the XML via a `scheme` tag (descending from `font`) whose `val` attribute can be either `major` or `minor`. Accordingly, this PR, in addition to defining the Theme Font properties, adds a `scheme` property, with getter and setter, to Style/Font.
The main benefit of this PR is that you can now load and save a spreadsheet preserving the connections to the Theme Fonts, without having to take any additional action.
A secondary benefit arises from the following difference. Empty cells in Excel will use the spreadsheet's default font name when they are filled in; but, in Google Sheets, they will use the Theme Minor Font name. By setting the `scheme` property in the default style, the resulting spreadsheet will behave the same in both Excel and Google.
I will note that Excel's font themes specify a Latin font, an East Asian font, a Complex Scripts font, and a set of font substitutions for various languages. PhpSpreadsheet will preserve all of these, and allow them to be changed. However, although it is easy to imagine how the non-Latin options might work, I have not yet been able to come up with an example where Excel uses any of them. In particular, if I use a theme font which does not support language X, and I use Language X in a cell bound to the theme, Excel will use a substitution font which does support it, but the font which it uses does not seem to be chosen from the alternatives supplied in the theme.
* Scrutinizer
The sun rises in the east, and Scrutinizer issues more false positives.