[chore] media and emoji refactoring (#3000)

* start updating media manager interface ready for storing attachments / emoji right away

* store emoji and media as uncached immediately, then (re-)cache on Processing{}.Load()

* remove now unused media workers

* fix tests and issues

* fix another test!

* fix emoji activitypub uri setting behaviour, fix remainder of test compilation issues

* fix more tests

* fix (most of) remaining tests, add debouncing to repeatedly failing media / emojis

* whoops, rebase issue

* remove kim's whacky experiments

* do some reshuffling, ensure emoji uri gets set

* ensure marked as not cached on cleanup

* tweaks to media / emoji processing to handle context canceled better

* ensure newly fetched emojis actually get set in returned slice

* use different varnames to be a bit more obvious

* move emoji refresh rate limiting to dereferencer

* add exported dereferencer functions for remote media, use these for recaching in processor

* add check for nil attachment in updateAttachment()

* remove unused emoji and media fields + columns

* see previous commit

* fix old migrations expecting image_updated_at to exists (from copies of old models)

* remove freshness checking code (seems to be broken...)

* fix error arg causing nil ptr exception

* finish documentating functions with comments, slight tweaks to media / emoji deref error logic

* remove some extra unneeded boolean checking

* finish writing documentation (code comments) for exported media manager methods

* undo changes to migration snapshot gtsmodels, updated failing migration to have its own snapshot

* move doesColumnExist() to util.go in migrations package

internal/processing/common/common.go

@@ -20,6 +20,7 @@ package common
 import (
 	"github.com/superseriousbusiness/gotosocial/internal/federation"
 	"github.com/superseriousbusiness/gotosocial/internal/filter/visibility"
+	"github.com/superseriousbusiness/gotosocial/internal/media"
 	"github.com/superseriousbusiness/gotosocial/internal/state"
 	"github.com/superseriousbusiness/gotosocial/internal/typeutils"
 )
@@ -29,6 +30,7 @@ import (
 // processing subsection of the codebase.
 type Processor struct {
 	state     *state.State
+	media     *media.Manager
 	converter *typeutils.Converter
 	federator *federation.Federator
 	filter    *visibility.Filter
@@ -37,12 +39,14 @@ type Processor struct {
 // New returns a new Processor instance.
 func New(
 	state *state.State,
+	media *media.Manager,
 	converter *typeutils.Converter,
 	federator *federation.Federator,
 	filter *visibility.Filter,
 ) Processor {
 	return Processor{
 		state:     state,
+		media:     media,
 		converter: converter,
 		federator: federator,
 		filter:    filter,