[BUG] Web Features API omits mobile support information

[jamesnw]

Describe the bug

The get_feature endpoint uses the defaultBrowsers set.

webstatus.dev/backend/pkg/httpserver/get_feature.go

Line 36 in 91c1655

defaultBrowsers(),

This omits mobile browsers, which are taken into account for baseline status.
https://github.com/GoogleChrome/webstatus.dev/blob/main/backend/pkg/httpserver/server.go#L106-L113

To Reproduce
Steps to reproduce the behavior:

1. Load https://api.webstatus.dev/v1/features/paint-order
2. See that mobile browser information is not included

Expected behavior
Support information for android_chrome, firefox_chrome and safari_ios should be included.

Additional context
This is causing issues with the baseline-status web component, which renders paint-order as limited availability, but with all green checkmarks, as Safari iOS does not support it.

web-platform-dx/baseline-status#46

[jcscottiii]

Notes for self

We also need to ingest the data before we can actually show it.

We still get browser release info from BCD

webstatus.dev/lib/gcpspanner/spanneradapters/bcdconsumertypes/types.go

Lines 35 to 40 in 214db6d

	const (
	Chrome BrowserName = "chrome"
	Edge BrowserName = "edge"
	Firefox BrowserName = "firefox"
	Safari BrowserName = "safari"
	)

Then when we need to handle the mobile cases here when we get the data from web features

webstatus.dev/lib/gcpspanner/spanneradapters/web_features_consumer.go

Lines 149 to 179 in 214db6d

	func extractBrowserAvailability(
	featureData web_platform_dx__web_features.FeatureValue) []gcpspanner.BrowserFeatureAvailability {
	var fba []gcpspanner.BrowserFeatureAvailability
	support := featureData.Status.Support
	if support.Chrome != nil {
	fba = append(fba, gcpspanner.BrowserFeatureAvailability{
	BrowserName: "chrome",
	BrowserVersion: *support.Chrome,
	})
	}
	if support.Edge != nil {
	fba = append(fba, gcpspanner.BrowserFeatureAvailability{
	BrowserName: "edge",
	BrowserVersion: *support.Edge,
	})
	}
	if support.Firefox != nil {
	fba = append(fba, gcpspanner.BrowserFeatureAvailability{
	BrowserName: "firefox",
	BrowserVersion: *support.Firefox,
	})
	}
	if support.Safari != nil {
	fba = append(fba, gcpspanner.BrowserFeatureAvailability{
	BrowserName: "safari",
	BrowserVersion: *support.Safari,
	})
	}
	return fba
	}