Unresolved promise in ECSchemaRpcLocater.getSchemaSync

[laurynas111]

Describe the bug
SchemaContext.getSchemaSync throws an exception possibly due to a bug of how Promises are handled in ECSchemaRpcLocater.getSchemaSync

To Reproduce

1. Call SchemaContext.getSchemaSync method
2. An error with "An ECSchema is missing the require 'name' attribute" message is thrown

Expected behavior
Schema should be loaded Synchroniously

Desktop (please complete the applicable information):

• OS: Windows 10
• iTwin Studio 1.0.133
• iTwin.js Version 4.10.6

Additional context
schemaJson is an instance of Promise. And is passed to Schema.fromJsonSync method.

Since Schema.fromJsonSync can accept any object type, typescript compiler loses all info that the passed object is a Promise and is passed to reader.readSchemaSync as rawSchema

The promise is then being treated as SchemaProps object which results in an exception

itwinjs-core/core/ecschema-metadata/src/Deserialization/JsonParser.ts

Line 64 in 9a1fa6e

if (undefined === this._rawSchema.name)

[ColinKerr]

I propose that we just replace the sync implementation with code that throws right away. You should only use the async method when locating a schema over rpc/http.