#2623 Codegen/AWS: create-only required fields block list/get/delete in generated AWS models

Follow-up to swamp-club #2287, which fixed this for GCP in PR 341 (codegen/gcp/pipeline.ts nonCreatePathParams, and the create/update templates in codegen/gcp/extensionModelGenerator.ts).

swamp validates the whole GlobalArgsSchema whenever any global argument is set. This generator emits fields that only the create request needs as required there, so read-only methods fail unless callers pass placeholder create values.

Apply the same rule as #2287:

• Keep required only what a non-create method reads from globalArgs, plus synthetic instance names.
• Make create-only required fields optional in GlobalArgsSchema.
• Enforce them with a generated check at the start of create that throws create requires global arguments: before any API call.
• Where update fully replaces the resource (PUT), fill those fields from globalArgs, then from stored state, and throw before the API call if neither has them.
• Regenerate the provider twice (the second run must produce zero diff) and update the provider's design doc.

Required-ness is decided in codegen/aws/pipeline.ts, which passes cfSchema.required to the shared codegen/shared/zodGenerator.ts (the top-level required list there is only a recursion pass-through, so the AWS caller can pass a reduced list without changing nested output).

Example: model/aws/ec2 route requires RouteTableId in GlobalArgsSchema, but its list method reads only credentials from globalArgs and takes the parent filter from the resourceModel argument.

Notes:

• The synthetic name field stays required.
• update and sync read identifiers from stored state.
• update merges every defined globalArgs value into desiredState.
• codegen/designs/aws.md (Required fields from cfSchema.required are non-optional) needs updating.