Deprecate getAssetEmitter and recommend calling createAssetEmitter directly

[timotheeguerin]

fix #3397

Problem with calling getAssetEmitter is it create an asset emitter with the instance of the compiler used in the compilation and not the instance of the compiler defined in the type emitter necessarly. This cause issue with instanceof checks which are then not the exact same class as its loaded form different instance of the compiler
Calling createAssetEmitter solve the issue because it is imported in teh context of the emitter package and will use the emitter package version

[azure-sdk]

All changed packages have been documented.

• ✅ @typespec/compiler
• ✅ @typespec/json-schema
• ✅ @typespec/openapi3

Show changes

@typespec/compiler - fix ✏️

Deprecate getAssetEmitter and recommend calling createAssetEmitter directly

@typespec/json-schema - fix ✏️

Fix issue that could result in invalid document generation when running tsp compile from another directory

@typespec/openapi3 - fix ✏️

Fix issue that could result in invalid document generation when running tsp compile from another directory

[azure-sdk]

You can try these changes at https://cadlplayground.z22.web.core.windows.net/prs/3516/

Check the website changes at https://tspwebsitepr.z22.web.core.windows.net/prs/3516/