build: create custom bazel dev-server rule

[devversion]

Implements a custom bazel dev-server rule that can be exposed eventually. The reason
we need a custom dev-server implementation is that the "ts_devserver" is not flexible
and needs to be synced into google3 (causing slow PR turnaround; and hestitancy to adding
new features. always the question of scope: for example)).

We need our own implemenation because we want:

• Live-reloading to work (ts_devserver: ibazel livereloading if concatjs bundle is not used bazel-contrib/rules_nodejs#1036)
• HTML History API support (currently the ts_devserver always sends a 404 status code)
• Better host binding of the server (so that we can access the server on other devices)
• Flexibility & control (being able to do changes so that the dev-server fits our needs)

Note: we can talk about exposing this to the public, but that's something we can do afterwards too. Also once this lands, we can use it for the e2e-app as well.

This also makes #16935 unnecessary as the root-cause is fixed.

[devversion]

Test failures are caused by a merge conflict in master that will be solved in #16928.

[devversion]

@jelbourn @josephperrott Addressed feedback. Please have another look.

[jelbourn]

LGTM

[ngbot]

I see that you just added the pr: merge ready label, but the following checks are still failing:
     status "ci/circleci: tests_browserstack" is failing

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If you can't get the PR to a green state due to flakes or broken master, please try rebasing to master and/or restarting the CI job. If that fails and you believe that the issue is not due to your change, please contact the caretaker and ask for help.

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