Fix: setCursor doesn't work well with inputStyle: "contenteditable",

[A-312]

Fix: #6167

This PR fix ContentEditableInput.showSelection(info), I removed takeFocus because it always false. It is a remanent code, it cannot work like that.

Also, I add a demo page to try the spellchecker (and also, because I discovered that we can active the spellchecker only with stackoverflow, not with the codemirror documentation....).

My last change is to add options.forceFocus because the behavior of selection in the ContenteditableInput editor with no focus is weird and different of the behavior that we get with TextareaInput.

Q/A

Q/A setSelection

To test my PR/fix you have to go on demo/abc.html and try to do :

• editor.setSelection({line:0, ch:2}, {line:0, ch:5})
• editor.setCursor({line:0, ch:2})

Try each time with focus (--> click in the editor) and without no focus (--> click out of the editor, in the page)

Q/A options.forceFocus

To test options.forceFocus:

1. Select a word on demo/abc.html page, like this:
   
2. Try editor.setSelection({line:0, ch:2}, {line:0, ch:5}), nothing should be change.
3. Try editor.setSelection({line:0, ch:2}, {line:0, ch:5}, {forceFocus:true}), selection should be visible, like this:
   

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We have a visual difference between contenteditable and textarea InputStyle:

• TextareaInput: Selection is show with focus or not focus ;
• ContenteditableInput: Selection is only show if the editor has focus.