Package declaration file for commonjs packages

[rbuckton]

Implements #3089.

• Adds a packageName compiler option, used to specify the name of the package.
• Adds a packageMain compiler option, used to specify the path to the main typescript module for the package.
• Adds a packageDeclaration compiler option, used to specify the output path of the declaration file for the package.
• Adds a packageDir compiler option to control the root directory of the package (falls back using: rootDir, the common directory path, the current directory).
• When the first three options above are supplied and either module or a target of ES6, we should emit a single declaration file for the program inputs over and above any individual declaration files generated if declaration is specified.

The output for a packageDeclaration would have the following form:

• Exports for the main module will be defined inside of an ambient external module that has the name provided via packageName.
• Exports for relative modules will be defined inside of an ambient external module that has a name derived from the package name, and the path of the module relative to the package directory, the supplied rootDir, the common directory path, or the current directory.

[aboeglin]

What is the status on this ?

[mhegazy]

@aboeglin this is tracked by #4433 now.

[mhegazy]

closing in favor of #4433