Migration: fix pubspec deps.

The previous deps had never been validated and were wrong in many ways
(for some deps the constraint was too narrow or too wide; other deps
were missing or extraneous).  I did some experimenting with `pub get`
and `pub run test` to find the earliest version of each package for
which the version solve succeeds and the tests pass.

Note, however, that nnbd_migration currently depends on unpublished
functionality from the _fe_analyzer_shared and analyzer packges.  So
before publishing nnbd_migration we'll need to publish
_fe_analyzer_shared and analyzer and then update the pubspec one last
time.

Change-Id: If8453226bfcc5e94ac84f1a3fdc0d2f4ee150f54
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/149661
Reviewed-by: Samuel Rawlins <srawlins@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>

pkg/nnbd_migration/pubspec.yaml

@@ -3,12 +3,23 @@ publish_to: none
 environment:
   sdk: '>=2.6.0 <3.0.0'
 dependencies:
-  _fe_analyzer_shared: ^2.0.0
-  analyzer: ^0.37.0
-  analyzer_plugin: ^0.2.2
+  # TODO(paulberry): fix _fe_analyzer_shared and analyzer deps once new versions
+  # are published.
+  _fe_analyzer_shared: ^3.0.0 # Actually need next version after this
+  analyzer: ^0.39.8 # Actually need next version after this
+  analyzer_plugin: ^0.2.4
+  args: ^1.4.4
+  charcode: ^1.1.2
   cli_util: ^0.1.4
+  collection: ^1.14.11
+  crypto: ^2.0.6
+  meta: ^1.1.6
   path: ^1.6.2
-  stream_channel: any
-  yaml: any
+  pub_semver: ^1.4.2
+  source_span: ^1.4.1
+  yaml: ^2.1.15
 dev_dependencies:
-  args: ^1.5.2
+  http: '>=0.11.3+17 <0.13.0'
+  test: ^1.6.4
+  test_core: '>=0.2.6 <0.4.0'
+  test_reflective_loader: ^0.1.8