Fix whitespace issues with block directive formatting

[mportiz08]

Bug/issue #, if applicable:

Summary

Fixes the following issues with block directive formatting

• top-level/starting block directive has unnecessary preceding newline
• top-level block directive is unexpectedly indented
• nested block directive has unnecessary newline before "}" character

For example:

import Markdown
print(Document(
    BlockDirective(name: "Metadata", children: [
        BlockDirective(name: "TitleHeading", argumentText: "Example")
    ])
).format())

Expected output:

@Metadata {
    @TitleHeading(Example)
}

Actual output:

    @Metadata {
        @TitleHeading(Example)
    }

Testing

Steps:

1. Create a new Snippet that calls format() on a document with block directives
2. Verify that the printed markdown doesn't exhibit the noted issues

Checklist

Make sure you check off the following items. If they cannot be completed, provide a reason.

• Added tests
• Ran the ./bin/test script and it succeeded
• Updated documentation if necessary

[mportiz08]

@swift-ci test

[QuietMisdreavus]

Can you also add a test for when a directive is after another element, like a heading?

[mportiz08]

Can you also add a test for when a directive is after another element, like a heading?

Yep

[mportiz08]

Added.

I also found another bug and fixed it as part of a more complex test.

[mportiz08]

@swift-ci test

[mportiz08]

@swift-ci test