clang-format: [JS] ASI after imports

Summary:
Automatic semicolon insertion should break import and export statements:

Before, this would format on one line:

  // Note: no semi after 'x' below!
  import {x} from 'x'
  export function foo() {}

Into:
  import {x} from 'x' export function foo() {}

With this change, the statements get separated.

This also improves automatic semicolon insertion to consider closing
braces preceding declarations and statements.

Reviewers: klimek

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D28465

llvm-svn: 291428