Revert "Revert "1. Remove unused dart debugger API entrypoints which are not used anymore""

This reverts commit e76ea5b.

1. Remove unused dart debugger API entrypoints which are not used anymore
   as this API has been deprecated and dartium was the last user.

2. Some unit tests are using some of these API entrypoints, so moved them
   over to a test file which will be linked into run_vm_tests

Change-Id: I5a486b98e4b97eb4df2e58d9cc0ba603e96c2e32
Reviewed-on: https://dart-review.googlesource.com/11180
Reviewed-by: Siva Annamalai <asiva@google.com>

Author: a-siva

runtime/BUILD.gn

@@ -187,7 +187,6 @@ template("libdart_library") {
       "include/dart_native_api.h",
       "include/dart_tools_api.h",
       "vm/dart_api_impl.cc",
-      "vm/debugger_api_impl.cc",
       "vm/mirrors_api_impl.cc",
       "vm/native_api_impl.cc",
       "vm/version.h",