Add codemod APIs from HackAST (FB project)

[fredemmott]

Key components:

• HackAstQuery - this is basically just a refactoring; for example, $hhast_node->getDescendantsOfType(HHAST\Foo::class) is largely the same as $hackast_node->query()->selectByType(HackAstFoo::class)
• HackCST* - this is a structured query language (but not actually SQL) for hh_server using hh_client --cst-search or hh_client --cst-search-files; this is depended on by HackASTQuery, and can also be used to reduce the number of files that a codemod needs to inspect
• HackAstMatcher - this is another query approach, allowing sscanf()-style patterns. For example, $matcher = await HackAstMatcher::genFromStmt('list(%s) = await genva(%s);'); $nodes = $ast->query()->selectByMatcher($matcher)->nodes() This ultimately allows reimplementing something similar to spatch on top of the AST.

HackCST* and HackAstMatcher have standalone benefits for HHAST in usability in performance; HackAstQuery would make it easier to port FB-internal codemods.