Enable no-unchecked-record-access rule for map

[RishhiB]

ESLint Configuration Changes:

• Changed the rule for @fluid-internal/fluid/no-unchecked-record-access from "warn" to "error" in the .eslintrc.cjs file by removing the line

Needs Review:

• Updated test assertions in directory.spec.ts to use optional chaining:
  • Changed value[0] to value?.[0] and value[1] to value?.[1] in multiple test cases for both fooSubDir and fooSubDir2 iterator results
• Modified serialize function to use optional chaining when accessing tree properties:
  • Changed header.type to header?.type
  • Changed header.content to header?.content

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

[jason-ha]

? doesn't make a difference to type checking. Should probably also remove the ? allowance in the linter rule (like removing T | undefined).
? is permissible to use in test code (in simple equality assertion checks).
To fix this ! could be used.
For packages that only have issues in test code, could move the warning to test only.