cmd/gomobile: add modulemaps to framework bundles for simpler imports
cmd/gomobile: add modulemaps to framework bundles for simpler imports

Modulemaps allow users to use the import directives without
providing the specific header file but by using a module name
in Objective-C and Swift.

  gomobile bind -target=ios golang.org/x/mobile/example/bind/hello

Add the generated framework to an Xcode project. You will be able
to import the library header and use the library by importing hello
in Swift.

  import hello
  // ...
  hello.GoHelloGreetings("burcu");

In Objective-C, you will be able to import with the module name
similarly by using the import directive below.

  #import hello

This CL also enables Go bindings to be used from Swift without an
Objective-C bridging header.

Fixes golang/go#12422

Change-Id: I7c60349caad100861d0b642ddfa873d7ada47598
Reviewed-on: https://go-review.googlesource.com/15044
Reviewed-by: Hyang-Ah Hana Kim <d7e82c3c07f92613bcbf9a1e88f6b96c13caa3b0@gmail.com>

xing/gomobile,xing/gomobile,0x90sled/mobile,golang/mobile,golang/mobile,0x90sled/mobile,0x90sled/mobile,xing/gomobile,0x90sled/mobile,0x90sled/mobile,golang/mobile,golang/mobile,xing/gomobile,xing/gomobile