Adds a test that verifies that the view of the local time is the same in
the Dart isolate and the process that is running the test.

Specifically, this test is useful to verify that the code paths for
timezone retrieval do not break while the underlying FIDL protocols are
being refactored.

However, since the check is generally useful, the test is written as a
general flutter test.

Running this on Fuchsia required adding `fuchsia.intl.ProfileProvider`
to the CMX file that is used for all build Fuchsia packages.

Testing is a bit involved on Fuchsia.  You must build the Fuchsia
package `fluter/shell/common:shell_tests` and publish it to the dev
repository for your Fuchsia device.  It seems that a way to do so is to
modify the script `flutter/tools/fuchsia/build_fuchsia_artifacts.py` and
modify its function `GetTargetsToBuild` like so:

```
def GetTargetsToBuild(product=False):
  targets_to_build = [
    'flutter/shell/platform/fuchsia:fuchsia',
    'flutter/shell/common:shell_tests',
  ]
  return targets_to_build
```

Next, the Fuchsia packages need to be compiled and published.

Once done, the following `fx` invocation will run the test, assuming
that you have your Fuchsia setup:

```
fx shell run \
    fuchsia-pkg://fuchsia.com/shell_tests#meta/shell_tests.cmx \
    -- --gtest_filter=ShellTest.LocaltimesMatch
```