Added "check-preblock" option to whitespace rule

[cameron-mcateer]

Also added fixes for inserting spaces and updated tests

PR checklist

• Addresses an existing issue: #0000
• New feature, bugfix, or enhancement
  • Includes tests
• Documentation update
• Enable CircleCI for your fork (https://circleci.com/add-projects)

What changes did you make?

I added the option to verify there is whitespace immediately before the opening brace of a block node. I also added fixes for the missing whitespace characters.

[adidahiya]

nice, this looks like a good rule option.

how does it handle plain blocks?

{
    const foo = 123;
    // code that just wants to be encapsulated in a block scope
}

[cameron-mcateer]

@adidahiya Good question! I added a couple examples to the test to show that they still pass.

[nchen63]

@cameron-mcateer Looks good, thanks

[glen-84]

This seems to be covered by the one-line rule (with the check-whitespace option).

Unfortunately, neither of these rules check the number of spaces (see #628).