[go_router] Fix Android Cold Start deep link with empty path losing scheme and authority.

[nozomemein]

Description

Fixes an issue where deep links with empty paths (e.g., https://example.com) lose their scheme and authority information during Android Cold Start.

This PR fixes flutter/flutter#174249

Detailed reproduction steps, environment information, and code sample are provided in the linked issue.

Problem

On Android Cold Start, if the initial deep link has no path (https://example.com),
_effectiveInitialLocation incorrectly creates a new Uri with only /? instead of preserving scheme and authority.
This results in the router receiving a relative path instead of the full deep link URL.

Solution

Use Uri.replace(path: '/') instead of creating a new Uri, so that the original scheme and authority are preserved.

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[chunhtai]

LGTM

[chunhtai]

I think this todo is obsolete now, can you remove this todo?

[nozomemein]

deleted in the commit below!

• 84da17c

[hannah-hyj]

LGTM

[nozomemein]

@hannah-hyj @chunhtai
Appreciate the approval!
I see there is a merge conflict. The contributor guide notes it’s fine to leave conflicts until the end of review, but I’m happy to rebase and resolve them now if that helps move this forward.
Please let me know which you’d prefer, and if there are any remaining blockers before landing.