Fix http requests to use read timeout in addition to connect timeout.

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• The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/CONTRIBUTING.md#commit-messages.
• There is an issue for the bug/feature this PR is for. To avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it.
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• All existing tests are passing: https://github.com/NativeScript/NativeScript/blob/master/DevelopmentWorkflow.md#running-unit-tests.
• Tests for the changes are included - https://github.com/NativeScript/NativeScript/blob/master/WritingUnitTests.md.

What is the current behavior?

Http timeout doesn't work as expected #6523 . When timeout is set, the request times out only if connection is not established within the timeout threshold.

What is the new behavior?

When timeout is set, the request will time out when the request has not completed within the timeout threshold. This can be due to failed connection or a response that takes too long to finish.
Fixes/Implements/Closes #6523 .

WIP - Writing Tests

I'm not sure how I should proceed with regard to writing the tests for a few reasons:

• In what module should I write the test(s)? http?
• I don't have an iOS device to test with.
• To test that a request connects but then fails due to not completing would require some stable URL whose response takes at least a set amount of time.