[feature] support processing of (many) more media types (#3090)

* initial work replacing our media decoding / encoding pipeline with ffprobe + ffmpeg

* specify the video codec to use when generating static image from emoji

* update go-storage library (fixes incompatibility after updating go-iotools)

* maintain image aspect ratio when generating a thumbnail for it

* update readme to show go-ffmpreg

* fix a bunch of media tests, move filesize checking to callers of media manager for more flexibility

* remove extra debug from error message

* fix up incorrect function signatures

* update PutFile to just use regular file copy, as changes are file is on separate partition

* fix remaining tests, remove some unneeded tests now we're working with ffmpeg/ffprobe

* update more tests, add more code comments

* add utilities to generate processed emoji / media outputs

* fix remaining tests

* add test for opus media file, add license header to utility cmds

* limit the number of concurrently available ffmpeg / ffprobe instances

* reduce number of instances

* further reduce number of instances

* fix envparsing test with configuration variables

* update docs and configuration with new media-{local,remote}-max-size variables

vendor/golang.org/x/net/context/context.go

@@ -1,56 +0,0 @@
-// Copyright 2014 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// Package context defines the Context type, which carries deadlines,
-// cancelation signals, and other request-scoped values across API boundaries
-// and between processes.
-// As of Go 1.7 this package is available in the standard library under the
-// name context.  https://golang.org/pkg/context.
-//
-// Incoming requests to a server should create a Context, and outgoing calls to
-// servers should accept a Context. The chain of function calls between must
-// propagate the Context, optionally replacing it with a modified copy created
-// using WithDeadline, WithTimeout, WithCancel, or WithValue.
-//
-// Programs that use Contexts should follow these rules to keep interfaces
-// consistent across packages and enable static analysis tools to check context
-// propagation:
-//
-// Do not store Contexts inside a struct type; instead, pass a Context
-// explicitly to each function that needs it. The Context should be the first
-// parameter, typically named ctx:
-//
-//	func DoSomething(ctx context.Context, arg Arg) error {
-//		// ... use ctx ...
-//	}
-//
-// Do not pass a nil Context, even if a function permits it. Pass context.TODO
-// if you are unsure about which Context to use.
-//
-// Use context Values only for request-scoped data that transits processes and
-// APIs, not for passing optional parameters to functions.
-//
-// The same Context may be passed to functions running in different goroutines;
-// Contexts are safe for simultaneous use by multiple goroutines.
-//
-// See http://blog.golang.org/context for example code for a server that uses
-// Contexts.
-package context // import "golang.org/x/net/context"
-
-// Background returns a non-nil, empty Context. It is never canceled, has no
-// values, and has no deadline. It is typically used by the main function,
-// initialization, and tests, and as the top-level Context for incoming
-// requests.
-func Background() Context {
-	return background
-}
-
-// TODO returns a non-nil, empty Context. Code should use context.TODO when
-// it's unclear which Context to use or it is not yet available (because the
-// surrounding function has not yet been extended to accept a Context
-// parameter).  TODO is recognized by static analysis tools that determine
-// whether Contexts are propagated correctly in a program.
-func TODO() Context {
-	return todo
-}