Add support for approximate geolocation

[alvinjiooo]

This commit introduces the ability for users and developers to request a less precise, privacy-preserving "approximate" location.

Key changes include:

• A new accuracyMode option in PositionOptions to request either "precise" or "approximate" location.
• A new geolocation-approximate permission and policy, which is implicitly granted if the "geolocation" permission is given.
• Separate internal caching for precise and approximate positions.
• Updated "Request a position" and "Acquire a position" algorithms to handle the new accuracy levels, permission fallback, and caching logic.
• The GeolocationPosition interface now includes an accuracyMode attribute to reflect the accuracy of the returned position.
• Expanded the introduction with a non-normative description of what an "approximate location" is.
• Added a normative privacy requirement for user agents to mitigate precise location reconstruction by caching approximate locations for a period of time.

Closes #182

Approximate Geolocation explainer

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Preview | Diff

[reillyeon]

For readability as you iterate on this proposal it's okay for this PR to directly change the specification text however to land this change the changes need to be enclosed in the correct candidate additions/corrections/deletions syntax.

[marcoscaceres]

@reillyeon if it's ok, let's move this to CR first (i.e., let's not waste time with the ins/dels). We are close to publishing as CR again.

[Copilot]

Pull Request Overview

This PR adds support for approximate location positioning to the Geolocation API specification. It introduces a privacy-preserving alternative to precise location sharing, allowing applications to request coarse-grained location data when high accuracy is not needed.

Key changes:

• Introduces accuracyMode option with "precise" (default) and "approximate" values
• Adds new "geolocation-approximate" permission alongside existing "geolocation" permission
• Implements separate caching for precise and approximate positions
• Updates permission request flows to allow users to choose between precise and approximate location sharing

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[antosart]

A few comments wrt the permission handling.

[marcoscaceres]

Please remove all the "Candidate addition" stuff. We don't need any of that additional markup anymore (but leave the rest of normative text there 😄 ) .

[antosart]

You should somehow make sure that effectiveAccuracy is approximate if in the api call accuracyMode: approximate was passed. I think this step is missing, since here you are just getting the maximum accuracy permission granted by the user. Or am I missing something?

[antosart]

Because of explainers-by-googlers/approximate-geolocation#19 and explainers-by-googlers/approximate-geolocation#20 I don't think we can make the policy-controlled feature geolocation-approximate work as expected. I suggest dropping it from this PR and we'll see whether we can fix things later on. WDYT?