JavaScript Backend: add JS parser for FFI imports

Description

GHCJS FFI uses a parser to support some JS forms that are not function calls: e.g. $1.property = $2

Using a function call for this kind of code induces some costs (runtime, code size) that we want to avoid. We need a JS parser to support these forms.

Tests affected by this issue

• ffi006 !11525 (closed)
• ffi008
• ffi011 !11525 (closed)
• ffi013
• ffi018
• ffi019
• ffi020
• ffi021
• ffi023
• T15933