New if_else_match_braces_linter

[MichaelChirico]

Part of #962

We might consider this one to be a default linter btw, it's basically part of the style guide.

[AshesITR]

In favor of making this a default linter, although I don't see explicit mention of this rule in https://style.tidyverse.org/syntax.html#control-flow
@jimhester, @hadley WDYT? Should we lint

if (test) a else {
  long_code
}

if (test) {
  long_code
} else a

by default?

[MichaelChirico]

FWIW styler agrees:

styler::style_text('if (test) a else {
  long_code
}

if (test) {
  long_code
} else a
')
# if (test) {
#   a
# } else {
#   long_code
# }

# if (test) {
#   long_code
# } else {
#   a
# }

[hadley]

Yeah this is definitely required by tidyverse style.

[MichaelChirico]

OK, done

[AshesITR]

LGTM