Formatter: String interpolation with macro expansion

[straight-shoota]

When a string interpolation contains a macro expansion, it results in three consecutive curly braces: "#{{{ macro_expression }}}". Having spaces in between helps reading the code: "#{ {{ macro_expression }} }".
The formatter currently removes those spaces. I think it should rather add them when missing to improve readability.

[waj]

Should it add space also for other expressions with curly braces? (tuples, hashes)