Graph-based CSS chunking now available behind experimental flag

Core Changes

• [Turbopack] Add graph-based CSS chunking algorithm behind experimental.cssChunking: "graph": #93606

Misc Changes

• Convert more tests from createNext -> nextTestSetup: #93799
• turbopack: emit assets before duplicate check in emit_assets: #93875
• [test] split og-api test suite into default and standalone variants: #93915
• Pass projectDir to adapter modifyConfig: #93916
• Distinguish in-navigation errors in the instant error overlay: #93843
• Eval next.config export functions in the try catch: #93884
• Rename TaskExecutionReason::Initial to Root: #93922

Credits

Huge thanks to @timneutkens, @sokra, @unstubbable, @mischnic, @aurorascharff, and @lukesandberg for helping!