Fix bug with increment read window (awslabs#535)

**Issue:**
Turns out, if `aws_channel_slot_increment_read_window()` was called while the "window update task" was running, the "window update task" would not get rescheduled to run again.

I was writing read-window-update tests for the python WebSocket bindings, and the test was failing as the read window approached 0. Here's how it played out:
- the WebSocket started with a read window of 500 bytes
- a 1000 byte payload (total frame size 1004) was sent to the WebSocket
- the HTTP handler sent along the first 500/1004 bytes
- the WebSocket processes this, but since the first 4 bytes were frame metadata that it doesn't count against the read window, it increments its read window by 4 bytes
- but due to this bug, the "window update task" DOES NOT get rescheduled
- and my test would fail because it received 4 less bytes than it expected

**Description of changes:**
Fix rescheduling logic for "window update task"

Add new SeekFailed, GetLengthFailed, GetLengthUnsupported, and SeekUn…

…supported Errors (awslabs#530)

Create setter for TLS Cipher Preference for use by C++ CRT SDK (awsla…

…bs#531)

Update CI to fix downstream build (awslabs#525)

Fix C++ One Definition Rules (ODR) Violations (awslabs#528)

**Issue:**
aws/aws-sdk-cpp#2137

**Description of Changes:**
Rename private `write_request` struct avoid collisions with same-named struct in other .c files

Set thread names to help debugging (awslabs#519)

Also, rename a few choice functions where people often think our code is deadlocked, but it's not.

Using CamelCase names like "AwsHostResolver" because 15 characters is the max for Linux, so we can't do "aws_host_resolver"

Use const in aws_host_resolver_new_default (awslabs#522)

Adds missing const in tls_channel_handler (awslabs#520)

Removes AWS_FATAL_ASSERT in s_aws_event_loop_group_shutdown_async (aw…

…slabs#515)

Fix for heap access violation (awslabs#513)

Fixes a heap access violation found when implementing AppVerifier into the C++ V2 SDK CI. Now the code correctly only frees the pcerts manually when required.