Option to choose spaces instead of tab

### Description

Currently the tab button returns a literal tab character. In most editors there is an option to convert a tab in to a number of spaces. White space indenting is important for e.g. Python, Nim, Haskell etc. Having to type 4 spaces is cumbersome, but I could not find an option to change it.

### Describe the solution you'd like

**Solution**
- An option for choosing the indentation character: Tab or Space
- An option for setting the amount of spaces when indenting with the Tab key

**Scintilla**
The documentation for the Scintilla editor for indentation are here: https://www.scintilla.org/ScintillaDox.html#TabsAndIndentationGuides

**SciTE**
In SciTE you can change the SciTEUser.properties file and insert:
```
tabsize=4 # Sets the width of a tab character to 4 spaces
indent.size=4 # Sets the indentation size to 4 spaces
use.tabs=0 # Ensures that pressing the Tab key inserts spaces instead of tab characters
```
Language specific settings, e.g. for Python, are set in a _python.properties_ file.
```
file.patterns.py=*.py
tab.size=4
indent.size=4
use.tabs=0
```

**NotepadNext**
For NotepadNext in `src/scintilla/.editorconfig` is set on line 4: indent_style = tab

I don't know how NotepadNext handles and stores preferences under "setting > preferences".

**Notepad++**
This is the Notepad++ setting for indentation:

### Describe alternatives you've considered

Macro feature, but that does not work sufficiently.