Pass top-level region through EC2TaskDefinition child resources

[corymhall]

Parent: #1933

awsx:ecs:EC2TaskDefinition exposes a top-level region input, but the implementation does not consistently thread that region through all child resources.

Known child/defaulted paths to audit:

• default log group creation
• task role creation
• execution role creation
• root aws.ecs.TaskDefinition resource
• any nested helper paths used by these defaults

Implementation references:

• awsx/schema-types.ts (EC2TaskDefinitionArgs.region)
• awsx/ecs/ec2TaskDefinition.ts
• awsx/cloudwatch/logGroup.ts
• awsx/role.ts

Acceptance criteria:

• top-level region is passed to all EC2 task-definition child AWS resources that support it
• region-aware invokes/lookups used by defaults receive the top-level region when present
• targeted tests cover the changed behavior