[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/github.com/go-xmlfmt/xmlfmt/xmlfmt.go

@@ -1,77 +0,0 @@
-////////////////////////////////////////////////////////////////////////////
-// Porgram: xmlfmt.go
-// Purpose: Go XML Beautify from XML string using pure string manipulation
-// Authors: Antonio Sun (c) 2016-2021, All rights reserved
-////////////////////////////////////////////////////////////////////////////
-
-package xmlfmt
-
-import (
-	"html"
-	"regexp"
-	"strings"
-)
-
-var (
-	reg = regexp.MustCompile(`<([/!]?)([^>]+?)(/?)>`)
-	// NL is the newline string used in XML output, define for DOS-convenient.
-	NL = "\r\n"
-)
-
-// FormatXML will (purly) reformat the XML string in a readable way, without any rewriting/altering the structure.
-// If your XML Comments have nested tags in them, or you're not 100% sure otherwise, pass `true` as the third parameter to this function. But don't turn it on blindly, as the code has become ten times more complicated because of it.
-func FormatXML(xmls, prefix, indent string, nestedTagsInComments ...bool) string {
-	nestedTagsInComment := false
-	if len(nestedTagsInComments) > 0 {
-		nestedTagsInComment = nestedTagsInComments[0]
-	}
-	reXmlComments := regexp.MustCompile(`(?s)(<!--)(.*?)(-->)`)
-	src := regexp.MustCompile(`(?s)>\s+<`).ReplaceAllString(xmls, "><")
-	if nestedTagsInComment {
-		src = reXmlComments.ReplaceAllStringFunc(src, func(m string) string {
-			parts := reXmlComments.FindStringSubmatch(m)
-			p2 := regexp.MustCompile(`\r*\n`).ReplaceAllString(parts[2], " ")
-			return parts[1] + html.EscapeString(p2) + parts[3]
-		})
-	}
-	rf := replaceTag(prefix, indent)
-	r := prefix + reg.ReplaceAllStringFunc(src, rf)
-	if nestedTagsInComment {
-		r = reXmlComments.ReplaceAllStringFunc(r, func(m string) string {
-			parts := reXmlComments.FindStringSubmatch(m)
-			return parts[1] + html.UnescapeString(parts[2]) + parts[3]
-		})
-	}
-
-	return r
-}
-
-// replaceTag returns a closure function to do 's/(?<=>)\s+(?=<)//g; s(<(/?)([^>]+?)(/?)>)($indent+=$3?0:$1?-1:1;"<$1$2$3>"."\n".("  "x$indent))ge' as in Perl
-// and deal with comments as well
-func replaceTag(prefix, indent string) func(string) string {
-	indentLevel := 0
-	return func(m string) string {
-		// head elem
-		if strings.HasPrefix(m, "<?xml") {
-			return NL + prefix + strings.Repeat(indent, indentLevel) + m
-		}
-		// empty elem
-		if strings.HasSuffix(m, "/>") {
-			return NL + prefix + strings.Repeat(indent, indentLevel) + m
-		}
-		// comment elem
-		if strings.HasPrefix(m, "<!") {
-			return NL + prefix + strings.Repeat(indent, indentLevel) + m
-		}
-		// end elem
-		if strings.HasPrefix(m, "</") {
-			indentLevel--
-			return NL + prefix + strings.Repeat(indent, indentLevel) + m
-		}
-		defer func() {
-			indentLevel++
-		}()
-
-		return NL + prefix + strings.Repeat(indent, indentLevel) + m
-	}
-}