A new `Golang` code generation handler was added. It is a very early
work-in-progress. Further development should happen mostly within
`lib/targets/golang`, adding new classes and completing the `emit`
handler to handle the element types.

Disclaimer: some of the currently generated code may not be valid Go...

Note: Naming packages by the go convention (see:
https://blog.golang.org/package-names) results in very long, hard to
read package names, so we may want to consider breaking from convention
and adding underscores, e.g.

…ang/code-generation

Structs and interfaces should not all be lowercased.

Also adds newline after writing to-level package name and removes extra
whitespace after method definitions.

TODO:
- Handle `any` type (does not exist in go)
- Handle type unions
- Capitalize any exported methods
- Handle method arguments

so that yarn build actually succeeds

ran yarn test:update

Expected output now lives in under the __snapshots__ dir

Fixes compiler errors on generated code with the following:

1. Return placeholder types from JSII class method calls
2. Prevent recursive structs by detecting types nested as properties
within themselves and use a pointer instead
3. Map TS `any` types to an empty struct `GoAny` to be provided by the
JSII runtime library
4. Fix `map` and slice type signatures in struct properties
5. Fix submodule struct and `package` names
6. Fix broken PascalCasing of return types in class methods when
returning a named JSII type

Also misc cleanup/enhancements:
1. Call a dummy NoOp method inside JSII class method calls provided by
runtime
2. Add import statement for runtime library to modules
3. Consolidate import statements

TODO: isDataType() in jsii-reflect seems wrong -- would be nice to
leverage this method in module.ts.

Add some doc comments and cleanup.

Changes the `Module` interface to an abstract base class that is
extended by `Package` and `Submodule` to avoid repeating module build
and emit logic.

Change dynamic getters for module submodules and types to be built and
set in constructor to avoid unecessary recomputation.

Minimizes changes to interface type for refactoring to class layout
based on struct/interface differences.

…ang/code-generation-ast

Adds a section about configuring GoLang code generation in
`docs/configuration.md`. Notes that go code generation is experimental
and is not suitable for production use.

Update snapshots.

Renames module related classes to be more idiomatic to go package output.

…ang/code-generation

BasePackage => Package
Package => RootPackage

Note: RootPackage could be thought of as "module", but we are reserving
that word due to "go mod"

Removes the embedded runtime logic until an appropriate alternative is
identified. The current strategy was causing the output byte array
inside the snapshots to differ from user to user based on build
environment.

Fixes casing in `goModuleName` util to be all lower case.