Split *ModuleContext out of module.go

Move EarlyModuleContext, BaseModuleContext and ModuleContext out of
module.go and into early_module_context, base_module_context and
module_context.go respectively.

Test: builds
Change-Id: I52e6eb1589d1478233c1c55d770b395a16eaa1a3

android/Android.bp

@@ -37,6 +37,7 @@ bootstrap_go_package {
         "api_levels.go",
         "arch.go",
         "arch_list.go",
+        "base_module_context.go",
         "bazel.go",
         "bazel_handler.go",
         "bazel_paths.go",
@@ -51,6 +52,7 @@ bootstrap_go_package {
         "defs.go",
         "depset_generic.go",
         "deptag.go",
+        "early_module_context.go",
         "expand.go",
         "filegroup.go",
         "fixture.go",
@@ -65,6 +67,7 @@ bootstrap_go_package {
         "makevars.go",
         "metrics.go",
         "module.go",
+        "module_context.go",
         "mutator.go",
         "namespace.go",
         "neverallow.go",