Support @Schema annotation for Object parameters in FunctionTool

Is your feature request related to a problem? Please describe.
Currently, adk-java relies on Jackson's @JsonProperty for defining schema names and required fields for pojos used as FunctionTool parameters. This creates several friction points:

1. Naming Conflicts: We may want the LLM-facing parameter name (e.g., snake_case) to differ from the Java field name (e.g., camelCase) without affecting internal JSON serialization used for other purposes.
2. Missing Metadata: Standard Jackson annotations do not support a description field, which is critical for FunctionTool schemas.
3. Ambiguous Optionality: Controlling whether a field is "required" or "optional" in the generated schema is difficult to decouple from Jackson's strict deserialization rules.

Describe the solution you'd like
I would like to extend the com.google.adk.tools.Annotations.Schema annotation to act as the highest source of truth for generating the FunctionTool schema in regards to pojo parameters, and deserialization. This includes:

1. Name: @Schema(name="...") should control the property name in the generated schema and during deserialization of the LLM response.
2. Description: @Schema(description="...") should populate the schema description.
3. Optionality: @Schema(optional=true/false) should explicitly control whether a field is marked as required, overriding Jackson's default behavior if necessary.

Describe alternatives you've considered

1. Jackson Mixins: We could use Jackson Mixins to separate the LLM view from the internal view, but this adds significant boilerplate and complexity for developers.
2. Custom Annotations: I considered creating a new set of annotations, but extending the existing @Schema annotation seems more idiomatic for the ADK.

Additional context
The Object FunctionTool parameter doesn't seem to have a direct 1-1 equivalent in adk-python, other than an issue requesting for pydantic models to be supported as FunctionTool parameters.

The precedence rules I believe align best with the rest of the library would be :

Name: @Schema(name) > @JsonProperty(value) > Field Name
Description: @Schema(description) > None
Required: @Schema(optional) > @JsonProperty(required) > Default (Optional)

These rules should not affect the way prior objects that have been passed without the @Schema annotation are treated.