Trim trailing spaces in editor before saving the content

Discussed in here gitlab-com/www-gitlab-com!2717 (closed)

We should trim trailing spaces in the line end before posting editor content to server. The code below should do the trim.

session = aceEditor.getSession()
doc     = session.getDocument()
lines   = doc.getAllLines()

for lineContent, lineNumber in lines
  trailingSpaceAt = lineContent.search /\s+$/

  if trailingSpaceAt > -1
    doc.removeInLine lineNumber, trailingSpaceAt, lineContent.length

finalContent = session.getValue()