Improve Swift indentation support

[ainame]

Summary

This updates Swift indentation support so that indent_size is applied to all relevant swift-mode indentation offsets:

• swift-mode:basic-offset
• swift-mode:multiline-statement-offset
• swift-mode:parenthesized-expression-offset

Previously, editorconfig-emacs only applied indent_size to swift-mode:basic-offset.

Background

This follows the discussion in swift-emacs/swift-mode#202.

Historically swift-mode has three separate indentation settings for Swift code: block indentation, multiline statement indentation, and parenthesized expression indentation. They are all customizable via defcustom in swift-mode:

https://github.com/swift-emacs/swift-mode/blob/5782bb9ab0773b5c6abddc23a14b82e5356cc2db/swift-mode-indent.el#L36-L52

In that discussion, we agreed that swift-mode should move towards using the same indentation value for these offsets by default. This PR applies the same idea on the editorconfig-emacs side: when a project provides indent_size, it should be applied to all three Swift indentation settings instead of only swift-mode:basic-offset.

This makes editorconfig-emacs handle all indentation settings exposed by swift-mode, so that a project-level indent_size can control Swift indentation consistently.

[monnier]

As the docstring says, editorconfig-indentation-alist is a fallback used for those modes which don't set editorconfig-indent-size-vars. So the better fix is to change swift-mode so it does something like:

(setq-local editorconfig-indent-size-vars
            '(swift-mode:basic-offset
              swift-mode:multiline-statement-offset
              swift-mode:parenthesized-expression-offset))

[ainame]

I see. I read the docstring and understood the context #383 now. I'll send a patch to swift-mode.el instead. Thank you for your reply!