Firebase Apple 12.15.0

The Firebase Apple SDK (12.15.0) is now available. For more details, see
the Firebase Apple SDK release notes.

To install this SDK, see Add Firebase to your project.

What's Changed

• [Core] Require swift-tools-version:6.1 in Package.swift by @andrewheard in #16223
• [AI] Rename GeminiModel to GeminiLanguageModel by @andrewheard in #16227
• fix(appcheck): remove redundant fac debug token logging by @ncooke3 in #16197
• feat(appcheck): Add new internal, default provider by @ncooke3 in #16190
• docs(appcheck): prefer 'AppCheckDebugToken' for debug env var injection by @ncooke3 in #16230
• feat(appcheck): add helpful log for registering debug tokens by @ncooke3 in #16232
• [AI] Add Hashable conformance to model config types by @andrewheard in #16233
• [AI] Add public init for GeminiLanguageModel by @andrewheard in #16234
• feat(ai): add app check dependency by @ncooke3 in #16185
• Readme improvements by @paulb777 in #16238
• [AI] Revert rename of GeminiModel to GeminiLanguageModel by @andrewheard in #16237
• Migrate repo dev content from README to CONTRIBUTING by @paulb777 in #16239
• [AI] Add readme banner for FMF adapter by @paulb777 in #16248
• Analytics 12.15.0 by @htcgh in #16250
• fix(firestore): remove designated initializers for force_index by @dlarocque in #16229
• fix(ai): Handle Xcode 27 LanguageModelSession.Error collision by @andrewheard in #16257
• feat(appcheck): implement RecaptchaEnterpriseProvider and tests by @ncooke3 in #16155
• [AI] Support SpeechConfig in Text-To-Speech by @milaGGL in #16226
• try building docc docs on swift package index by @morganchen12 in #16262

Full Changelog: 12.14.0...12.15.0