Changes in compiler output from 9.1.4 to current master

[cknitt]

I diffed the JS output from 9.1.4 to the output from the current master for one of our projects and noticed the following changes:

• 1. Some superfluous newlines are gone 👍
• 2. Superfluous returns (for functions returning unit) are gone. 👍
• 3. Output for template string literals is now different. If the template string literal starts/ends directly with a placeholder, a leading "" + / trailing + "" is added.
• 4. Promise handling is different, instead of promise.then(f) there is now Js_promise.then(f, promise), similarly for catch. This is normal because of the deprecation of @bs.send.pipe. Bindings in t-first style do not have this.
• 5. There are now some unnecessary variables generated, e.g.: (fix merged in master)
• 6. The printer now adds a newline after a switch case with braces (which are redundant anyway).
• 7. String.length not inlined anymore String.length not inlined in v10 #5480 (legit as strings are now unicode)

[cknitt]

Ah, and a very minor thing: The printer now adds a newline after a switch case with braces (which are redundant anyway).

[cristianoc]

Keeping this for reference in case something needs adding.