Rename capture_links to launch_handler

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https://github.com/WICG/sw-launch/blob/main/declarative_link_capturing.md#goals--use-cases

Capturing links and navigations from the following (non-exhaustive list of) sources:

• Clicked links from other web pages.
• URL launch from a native app in the operating system.
• Shortcuts API (jump lists to within the app)
• Protocol handlers
• File handlers
• Share Target API

Given the varied launch surfaces this spec is attempting to cover I think the capture_links field should be named more generally as launch_handler.
We can keep capture_links for web developers to configure link capturing specific matters e.g.: #30

[alancutter]

https://github.com/WICG/sw-launch/blob/main/launch_handler.md