Remove head-as-boolean emitter flag (superseded by TCGC @responseAsBool)

[Copilot]

The emitter flag head-as-boolean duplicates functionality now provided by TCGC's @responseAsBool decorator, which promotes the operation's response type to boolean directly. The flag is removed in favor of the decorator-based approach.

Changes

• src/lib.ts — Remove "head-as-boolean" from EmitterOptions interface and RLCOptionsSchema
• src/transform/transfromRLCOptions.ts — Remove headAsBoolean extraction and propagation
• src/modular/helpers/operationHelpers.ts:
  • isHeadAsBooleanOperation: drop context parameter and the legacy context.rlcOptions?.headAsBoolean fallback; now solely relies on TCGC's response.type.kind === "boolean" signal
  • buildNonModelResponseTypeDeclaration: remove dead code branch that handled void-HEAD with the emitter flag
• test/util/emitUtil.ts — Remove both head-as-boolean → headAsBoolean forwarding blocks
• test/modularUnit/scenarios/operations/wrapNonModelReturn.md — Remove 3 scenarios that drove behavior via head-as-boolean: true (covered by headResponseAsBool.md using @responseAsBool); strip head-as-boolean: false from remaining HEAD scenarios

Migration

Replace emitter option with the TCGC decorator on the operation:

-# tspconfig.yaml
-options:
-  "@azure-tools/typespec-ts":
-    head-as-boolean: true

+// main.tsp
+@Azure.ClientGenerator.Core.responseAsBool
 @head
 op checkExistence(@path name: string): void;