Message parsing and rendering - Phase 1 (#19654)

* Add escapeHTML helper

* Add unescapeHTML helper

* Move helpers to /lib

* Use the helpers

* feat/message-parsing

* Make escapeRegExp match its underscore.string counterpart

* Remove superfluous parameter

* Remove redundant function definition

* Work around oembed bug

* Refactor autolinker initialization

* Refactor autolinker initialization

* Refactor hexcolor initialization

* Refactor emoji initialization

* Refactor highlight-words initialization

* Refactor issuelinks initialization

* Refactor mentions initialization

* Refactor mapview initialization

* Remove trackSettingsChange module

* Remove some s.trim() usage

* Move renderMessageBody

* Move some renderMessage startup scripts

* Refactor katex startup

* Move some renderMessage startup scripts

* Move some spotify modules

* Fix reactivity

* Move spotify initialization

* Move markdown initialization

* Update Mocha configuration

* Rearrange renderMessageBody signature

* Move markdown template helpers

* Remove markdown template helpers

* Extract options from markdown

* Fix import

* Render message.location's mapview on message template

* Conditionally render message location

Co-authored-by: Guilherme Gazzo <guilherme@gazzo.xyz>