Remove getApp and getSettings calls from Message-Rendering (#4535)

* refactor: remove singletons from message rendering

* chore: add changelog entry

* Disable the `cppcoreguidelines-avoid-const-or-ref-data-members` clang-tidy check

* auto *app

* Selection is a struct, not a class

* Use ChannelView's `signalHolder_` instead of `channelConnections_`

* Remove `applySettings` step, instead just connect & set each setting individually

* rename & constify some context values

* Handle empty "last message color" setting value better (as it was
        originally in this pr before I removed that change :-)

* unrelated mini refactor cleanup

* let painSelection handle size_t instead of int

* Add some more comments to the MessageLayoutContext structs

---------

Co-authored-by: Rasmus Karlsson <rasmus.karlsson@pajlada.com>

src/common/Literals.hpp

@@ -24,7 +24,6 @@ namespace chatterino::literals {
 namespace detail {
     // NOLINTBEGIN(modernize-avoid-c-arrays)
     // NOLINTBEGIN(cppcoreguidelines-avoid-c-arrays)
-    // NOLINTBEGIN(cppcoreguidelines-avoid-const-or-ref-data-members)
 
     template <size_t N>
     struct LiteralResolver {
@@ -95,7 +94,6 @@ namespace detail {
         }
     };
 
-    // NOLINTEND(cppcoreguidelines-avoid-const-or-ref-data-members)
     // NOLINTEND(cppcoreguidelines-avoid-c-arrays)
     // NOLINTEND(modernize-avoid-c-arrays)