McpSchema.Tool should expose outputSchema via public accessor instead of requiring reflection

[sivakothuri]

When building CallToolResult for tools that declare an outputSchema, the SDK 0.17.2 requires structuredContent to be included in the response. However, there is no clean public API to check whether a McpSchema.Tool has an outputSchema set.

Currently, we are forced to use Java reflection to access the outputSchema field:
Object outputSchema = null; try { java.lang.reflect.Field field = tool.getClass().getDeclaredField("outputSchema"); field.setAccessible(true); outputSchema = field.get(tool); } catch (Exception e) { // No outputSchema field or access failed }

This approach is:

Fragile — breaks if the field is renamed or the class structure changes
Incompatible with module system — setAccessible(true) may fail under strict Java module rules (Java 17+)
Not idiomatic — McpSchema.Tool is a record, so it should already have an outputSchema() accessor

Expected Behavior:

McpSchema.Tool should expose a public outputSchema() method (or it already does as a record accessor, but it returns Map<String, Object> which may be null). The SDK should clearly document:

How to check if a tool has an outputSchema
Whether structuredContent is mandatory when outputSchema is present
Provide a utility or builder pattern that auto-handles the structured vs text content decision

Suggested Fix:

If Tool is a record, simply use tool.outputSchema() — document this clearly. If it's not exposed, add a public getter.