Follow-up comments to #15984

This updates AppContext per the recommendations in #15352

Fixes #15352

Some file I/O is piped from OS processes and never completes,
so without havign a timeout on the recording serialzation, we
end up waiting forever on that I/O to complete.

* Revert "Revert "Add android license verification to doctor and some refactoring" (#14727)"

This reverts commit d2602947.

* Add tests, fix sdkManagerEnv and use it consistently, and rearrange Status object model

* AnsiSpinner needs to leave the cursor where it found it.

* fix tests

* Const constructor warning only shows up on windows...?

* Avoid crash if we can't find the home directory

* Make pathVarSeparator return a string in the mock

* Implement review comments

* Fix out-of-order problem on stop

It was failing in the case of an AppContext being in scope
but not having a `BotDetector` seeded in it.

* Fix packages tests when run off bots

* Tweak dependencies to make bots happy

* Review comment

* Created plumbing but has stream problem

* testing with makePipe

* Trying pipe but not really getting anywhere

* works by repeatedly reading line

* Minor cleanup

* works

* Clean up pipe after use.

* Move the last status forward

* Make sure failed script commands bubble up

Reports from that commit included:

* Doctor hanging
* Doctor prompting to install JDK
* AnsiStatus.cancel() printing elapsed time and extra newline
* Printing extra spinner character at the end of each line

* Initial version, seems to work

* Unit test for android license checker

* Cleanups

* Windows analyzer wants const.

* Refinements to timeout

* review comments

* Forgot a nit

* Populate AnsiTerminal in context for daemon launches

* Strip out AnsiTerminal additions to context since they are no longer needed

Also some trivial improvements to style.

* Revert "Revert "Make artifact downloading more robust for flaky networks" (#13995)"

This reverts commit 33d8a035.

* Use subdirectories to organize cached files

* Fix unauthorized import

* Revert "Change github readme links to be served by github (#13929)"

This reverts commit fd516d95.

* Revert " Rename SemanticsFlags to SemanticsFlag (#13994)"

This reverts commit 24e3f705.

* Revert "Make artifact downloading more robust for flaky networks (#13984)"

This reverts commit 4d37e03e.

* First version

* Add a clarifying comment

* Add verify to ZipDecoder.decodeBytes call

* Review comments

* Need OS Error for missing files

* FileSystemException, not OSError.

* First version

* Prevent modification of .flutter during analytics test

* Pass in directory and override analyzer warning due to conditional import

* Review comments

* route device issue diagnostics to flutter doctor

* review comments

* review comments

I get this error when piping an `echo` string to the stdin of
the flutter tool.

https://github.com/dart-lang/sdk/issues/29083

I got tired of drive-by spelling fixes, so I figured I'd just take care of them all at once.

This only corrects errors in the dartdocs, not regular comments, and I skipped any sample code in the dartdocs. It doesn't touch any identifiers in the dartdocs either. No code changes, just comments.

If we fail to bind to IPv4 loopback, try IPv6. Some hosts only support IPv6,
causing the test in vmservice_test.dart to fail, since it couldn't find an
available port.

* enable lint prefer_asserts_in_initializer_lists

* enable --assert-initializer

* enable lint prefer_foreach

* fix tests

The initial loading happens on the host, which was building a script snapshot and allowing imports of dart:mirrors. Hot reload happens on the device, which then notices the imports and issues a compile-time error. This change causes programs with imports of dart:mirrors to be rejected during the initial load.

Fixes https://github.com/flutter/flutter/issues/12440

This class lives in the Context and allows callers to "inject"
flag values, where flag values are first extracted from the
command arguments, then from the global arguments as a fallback.

* round 2

* deal with null futures

* review

* review

* review

* review