Firefox previews fetch() keepalive support

[chrisdavidmills]

Summary

Firefox 132 ships the fetch() keepalive option in Nightly and early Beta builds.

This PR adds Fx preview support for api.fetch (as used for Window.fetch() and WorkerGlobalScope.fetch()) and Request.keepalive (doesn't yet have a docs page, but I'm going to change that).

It also adds a data point for the init.keepalive parameter of the Request() constructor, which just copies the same data from the other places.

See https://bugzilla.mozilla.org/show_bug.cgi?id=1906952 for the shipping bug.

Test results and supporting details

Related issues

Docs issue: mdn/content#36120

[caugner]

How did you determine the support status for the other browsers?

[chrisdavidmills]

I just copied the data for the init.keepalive parameter from the fetch.json data. They are two different ways of implementing the same thing (Request() constructor, versus directly inside the fetch() call), so they are going to be the same.

[caugner]

Thank you. Did you test the init.keepalive parameter in Node.js, or did you assume it's supported in the same version as the parent feature?

When comparing the data here against fetch.json, I noticed that there is no nodejs entry for the subfeature there, should we add it there?

browser-compat-data/api/_globals/fetch.json

Lines 195 to 233 in ad4f44f

	"init_keepalive_parameter": {
	"__compat": {
	"description": "<code>init.keepalive</code> parameter",
	"support": {
	"chrome": {
	"version_added": "66"
	},
	"chrome_android": "mirror",
	"deno": {
	"version_added": false
	},
	"edge": {
	"version_added": "15"
	},
	"firefox": {
	"version_added": false
	},
	"firefox_android": "mirror",
	"ie": {
	"version_added": false
	},
	"oculus": "mirror",
	"opera": "mirror",
	"opera_android": "mirror",
	"safari": {
	"version_added": "13"
	},
	"safari_ios": "mirror",
	"samsunginternet_android": "mirror",
	"webview_android": "mirror",
	"webview_ios": "mirror"
	},
	"status": {
	"experimental": false,
	"standard_track": true,
	"deprecated": false
	}
	}
	},

[chrisdavidmills]

Sure, added. I assumed that init.keepalive is just supported, the same as in the fetch() data.