.Net: Add public ctor for GeminiChatMessageContent with ToolCalls

[ionite34]

Motivation and Context

Fixes #12153

Since the IReadOnlyList<GeminiFunctionToolCall>? ToolCalls property of GeminiChatMessageContent is get only, and there is no public constructor accepting tool calls like there is for tool call results, it is currently not possible to recreate past history when loading context involving assistant messages with tool calls.

For manual tool invocation, it makes it impossible to recreate the last turn message for responding to the tool use manually.

This PR adds a public constructor to GeminiChatMessageContent accepting a IEnumerable<GeminiFunctionToolCall>

Description

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄

[ionite34]

@microsoft-github-policy-service agree