Add Google Pay golden request tests

[Max Harrison (maxharrison)]

The web Google Pay request had no structural fixture tests, so defaults and configured fields could drift from Android without a focused failure. googlePayGoldenRequest.test.ts now compares the web request projection with shared enabled-billing and custom fixtures, plus web-specific default and disabled-billing fixtures. The default and disabled-billing fixtures remain platform-specific because web and Android deliberately differ there until the planned major-release alignment.

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[Max Harrison (maxharrison)]

Superseded by a stack: #985 for the golden tests, #986 for the billingAddressParameters change. Splitting them keeps the production change out of a test-only PR and turns it into a visible fixture diff.