ref(core): Add shared type for build-time options

[s1gr1d]

Adds a Sentry-internal base interface for build-time options used in Sentry's meta-framework SDKs (e.g., Next.js, Nuxt, SvelteKit).

SDKs should extend this interface to add framework-specific configurations. To include bundler-specific options, this type can be combined with one of the Unstable[Bundler]PluginOptions types, such as UnstableVitePluginOptions or UnstableWebpackPluginOptions (also added in this PR)

import type { BuildTimeOptionsBase, UnstableVitePluginOptions } from '@sentry/core';
import type { SentryVitePluginOptions } from '@sentry/vite-plugin';

// Example of how a framework SDK would define its build-time options
type MyFrameworkBuildOptions =
  BuildTimeOptionsBase &
  UnstableVitePluginOptions<SentryVitePluginOptions> & {
    // Framework-specific options can be added here
    myFrameworkSpecificOption?: boolean;
  };

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Part of #14212