docs: improve documentation for function callback and tool context

- Add cross-references to tool context documentation section
- Enhance BiFunction section title and description
- Improve readability and consistency of function callback documentation

Author: tzolov

spring-ai-docs/src/main/antora/modules/ROOT/pages/api/function-callback.adoc

@@ -11,8 +11,8 @@ The main interface defines several key methods:
 * `getName()`: Returns the unique function name within the AI model context
 * `getDescription()`: Provides a description that helps the model decide when to invoke the function
 * `getInputTypeSchema()`: Defines the JSON schema for the function's input parameters
-* `call(String functionInput)`: Handles the actual function execution
-* `call(String functionInput, ToolContext toolContext)`: Extended version that supports additional context
+* `call(String functionArguments)`: Handles the actual function execution
+* `call(String functionArguments, ToolContext toolContext)`: Extended version that supports additional xref:api/functions.adoc#Tool-Context[tool context]
 
 == Builder Pattern
 
@@ -39,7 +39,9 @@ FunctionCallback callback = FunctionCallback.builder()
     .build();
 ----
 
-==== BiFunction<I, ToolContext, O> with ToolContext
+==== BiFunction<I, ToolContext, O> 
+
+Using Function with input type <I> and additional xref:api/functions.adoc#Tool-Context[ToolContext] parameter:
 
 [source,java]
 ----
@@ -113,7 +115,7 @@ The method invoking implements the `FunctionCallback` interface and provides:
 - Support for both static and instance methods
 - Any number of parameters (including none) and return values (including void)
 - Any parameter/return types (primitives, objects, collections)
-- Special handling for `ToolContext` parameters
+- Special handling for xref:api/functions.adoc#Tool-Context[ToolContext] parameters
 
 ==== Static Method Invocation
 
@@ -231,7 +233,7 @@ FunctionCallback.builder()
 
 === Tool Context Usage
 
-* Use ToolContext when additional state or context is required that is provided from the User and not part of the function input generated by the AI model.
+* Use xref:api/functions.adoc#Tool-Context[ToolContext] when additional state or context is required that is provided from the User and not part of the function input generated by the AI model.
 * Use `BiFunction<I, ToolContext, O>` to access the ToolContext in the function invocation approach and add `ToolContext` parameter in the method invoking approach.
 
 

spring-ai-docs/src/main/antora/modules/ROOT/pages/api/functions.adoc

@@ -378,6 +378,7 @@ String response = ChatClient.create(chatModel).prompt()
 The https://github.com/spring-projects/spring-ai/blob/main/models/spring-ai-openai/src/test/java/org/springframework/ai/openai/chat/client/OpenAiChatClientMethodInvokingFunctionCallbackIT.java[OpenAiChatClientMethodInvokingFunctionCallbackIT]
 integration test provides additional examples of how to use the FunctionCallback.Builder to create method invocation FunctionCallbacks.
 
+[[Tool-Context]]
 == Tool Context
 
 Spring AI now supports passing additional contextual information to function callbacks through a tool context.