Attribution tracking fails when configured via `autocapture.attribution`

## Expected Behavior
When configuring the SDK with `autocapture.attribution` settings, UTM parameters and other marketing
attribution data should be automatically tracked according to the documentation at
https://amplitude.com/docs/sdks/analytics/browser/browser-sdk-2

```javascript
amplitude.init(apiKey, undefined, {
autocapture: {
attribution: {
resetSessionOnNewCampaign: true,
},
},
});
```
This should capture UTM parameters (`utm_source`, `utm_medium`, etc.), referrer data, and click IDs when users visit with campaign parameters.

## Current Behavior

Attribution tracking silently fails when configured using only the autocapture property. UTM parameters are not captured, and no attribution events are sent to Amplitude.

The only way to get attribution working is to either:
1. Use the deprecated `@amplitude/plugin-web-attribution-browser` plugin, OR
2. Set both `autocapture` AND the deprecated `defaultTracking` property to the same configuration

## Possible Solution
The SDK has an inconsistency where some `autocapture` features check `config.autocapture` (correct) while others check the deprecated `config.defaultTracking` (incorrect).

Files that need to be fixed:

`packages/analytics-browser/src/browser-client.ts` - Update these lines to use `this.config.autocapture`
instead of `this.config.defaultTracking`:
- Line 172: Attribution tracking check
- Line 224: File download tracking check
- Line 229: Form interaction tracking check
- Line 235: Page view tracking check
- Lines 361, 381: Session tracking checks

`packages/analytics-browser/src/default-tracking.ts` - Update these functions:
- Lines 227-241: `getAttributionTrackingConfig()` should check `config.autocapture` instead of
`config.defaultTracking`
- Lines 188-225: `getPageViewTrackingConfig()` should check `config.autocapture` instead of
`config.defaultTracking`

Note: Commit 97969c32 on branch `AMP-125616/refactor-sr-observer-to-use-network-observer` already partially fixed this issue for network tracking but was never completed or merged.

## Steps to Reproduce
1. Initialize the SDK with autocapture attribution enabled:
```
import * as amplitude from '@amplitude/analytics-browser';

amplitude.init('your-api-key', undefined, {
autocapture: {
attribution: {
resetSessionOnNewCampaign: true,
},
},
});
```
2. Visit your application with UTM parameters:
` https://yourapp.com?utm_source=test&utm_medium=email&utm_campaign=spring2024`
3. Check the Amplitude event stream for the user
4. Observe: No UTM parameters are captured. Attribution tracking does not work.
5. Workaround: Add defaultTracking with the same config:
```
const config = {
attribution: {
resetSessionOnNewCampaign: true,
},
};

amplitude.init('your-api-key', undefined, {
autocapture: config,
defaultTracking: config, // Required for attribution to work
});
```
6. Repeat steps 2-3: Attribution now works correctly.

## Environment
- JS SDK Version: @amplitude/analytics-browser 2.29.0 (issue exists in all 2.x versions)
- Installation Method: npm and yarn
- Browser and Version: all browsers