ref(core): Add shared type for build-time options (#17151)

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)

```typescript
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;
  };
```

I created some interfaces for better high-level organization:
- `SourceMapsOptions`
- `ReleaseOptions`
- `BundleSizeOptimizationsOptions`

---

Part of #14212

Author: s1gr1d