Summary:The vast majority of `folly::dynamic` array initializations are
single-line and with no nested arrays, so we can fix them with a
syntactic codemod. This also fixes a couple of singletons.

For empty arrays:
```
codemod '((?:folly::)?)(dynamic\s+\w+\s*=\s*)({\s*})' '\1\2\1dynamic::array'
```

For non-empty ones:
```
codemod '((?:folly::)?)(dynamic\s+\w+\s*=\s*)(?:{\s*([^{}]+?)\s*})' '\1\2\1dynamic::array(\3)'
```

Reviewed By: igorsugak

Differential Revision: D3030338

fb-gh-sync-id: 3e56704a6c6294d6f6270e42a1776d991a7938df
shipit-source-id: 3e56704a6c6294d6f6270e42a1776d991a7938df