Introduce a composer reducer and move image state there (#5547)

* Add composer reducer

* Support adding images

Co-authored-by: Mary <git@mary.my.id>

* Support updating and deleting images

Co-authored-by: Mary <git@mary.my.id>

* Derive images state from composer state

Co-authored-by: Mary <git@mary.my.id>

---------

Co-authored-by: Mary <git@mary.my.id>

src/lib/api/index.ts

@@ -24,6 +24,7 @@ import {
   threadgateAllowUISettingToAllowRecordValue,
   writeThreadgateRecord,
 } from '#/state/queries/threadgate'
+import {ComposerState} from '#/view/com/composer/state'
 import {LinkMeta} from '../link-meta/link-meta'
 import {uploadBlob} from './upload-blob'
 
@@ -38,6 +39,7 @@ export interface ExternalEmbedDraft {
 }
 
 interface PostOpts {
+  composerState: ComposerState // TODO: Not used yet.
   rawText: string
   replyTo?: string
   quote?: {