Release 3.12.0

• #6062 [BUGFIX fetch] prevent Accept & ContentType header overwriting (#6062)
• 82743675 [BUGFIX release] Fix rollup warnings for require as an external module. (#6095)
• 545285f1 [BUGFIX release] Fix rollup warning for ember-inflector. (#6242)
• 48dd8120 [BUGFIX reload] fix sync belongsTo reload w/dematerialize (#6158)
• #6124 chore: remove co usage (#6124)
• #6155 Two small fixes to fetch (#6155)
• #6153 Fix yuidoc setup to support the split packages (#6153)
• #6078 Use HTML comments in PR template. (#6078)
• #6077 [BUGFIX release] Remove ember-fetch dependency. (#6077)
• #6112 [BUGFIX relationships] fix infinite retry bug for failed relationship fetches (#6112)
• #6125 [CHORE tests] replace mocha-only-detector with mocha/no-exclusive-tests rule (#6125)
• #6079 docs: fix RELEASE.md refs to publish.js
• #6247 [RFC 403] Identifiers Infra (#6247)
• #6274 [BUGFIX RELEASE] Fix generating from blueprints (#6274)
• #6168 [DOCS adapter] remove remaining sinceToken and update docs (#6168)
• #6181 Docs update for unloadRecord
• #6241 [BUGFIX release] Add blueprints to ember-data package.
• #6196 Docs: fixing request->record typo (#6196)
• #6252 [BUGFIX] Includes yuidoc's output data.json to published package
• #6281 [BUGFIX release] ensure all packages in correct RFC locations (#6281)
• #6256 [BUGFIX release] fix type overrides (#6256)
• #6250 [BUGFIX query] Remove arity check for adapter.query (#6250)
• #6280 [DOC release] Fix API doc issues with package split. (#6280)
• #6249 chore: refactor store to class (#6249)