Auto detect tab/indentation width, insert tab as spaces

[zufuliu]

Issue #299 implemented global, scheme and file levels tab settings, however, tab settings for current file (by default inherited from scheme or global settings) will confusing people when they not match the actually file. It's worthy to implement some sort of auto detection to reduce the confusing.

SciTE has a 50 lines detection method (SciTEBase::DiscoverIndentSetting() in SciTEIO.cxx), we can port it to Notepad2 with one change: drop support for tab width = 1, which is need to reliable detect Java code contains document comments (where the space before * is alignment space).

[zufuliu]

Implemented by f16ca83. The Tab Settings dialog needs translation.

[lifenjoiner]

There is an issue on diff/patch files:

[zufuliu]

Indentation width is set to be same as tab width, so I think this is detected.

[zufuliu]

It's might better to ignore detected tab/indentation width for binary file and diff file (them don't need to be detected), the result doesn't not make any sense:

1. Binary is loaded in read only mode (locked for editing).
2. In diff file, line starts with non-space character has specially meaning.

[lifenjoiner]

Yes, it is detected. But looks ... not good ...
What about making some exceptions (ignore detection) by scheme?

[lifenjoiner]

A draft/PoC lifenjoiner@303c4f2 calling FileVars_Apply(&fvCurFile) 1 more time

[lifenjoiner]

It is reasonable that:
fvCurFile is prepared and applied while loading file,
and EditDetectIndentation is a part of that;
also detecting/applying lexer after file loaded.

So, reset the inappropriate auto detected indentation results is reasonable, acting like manual.
Even if doing EditDetectIndentation after file loaded, it also requires 1 more calling of FileVars_Apply(&fvCurFile).

[zufuliu]

Binary file and diff file fixed by e64d89d.