ref(browser): Refactor isNativeFetch -> isNativeFunction

[billyvg]

This makes the isNativeFetch check a bit more generic/naive. It no longer checks that the function name matches fetch explicitly, but I think thats ok.

Follow-up to #11924

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser	21.74 KB (-0.16% 🔽)
@sentry/browser (incl. Tracing)	32.88 KB (-0.1% 🔽)
@sentry/browser (incl. Tracing, Replay)	68.25 KB (-0.03% 🔽)
@sentry/browser (incl. Tracing, Replay) - with treeshaking flags	61.67 KB (-0.03% 🔽)
@sentry/browser (incl. Tracing, Replay with Canvas)	72.28 KB (-0.03% 🔽)
@sentry/browser (incl. Tracing, Replay, Feedback)	84.33 KB (-0.02% 🔽)
@sentry/browser (incl. Feedback)	37.75 KB (-0.09% 🔽)
@sentry/browser (incl. sendFeedback)	26.31 KB (-0.13% 🔽)
@sentry/browser (incl. FeedbackAsync)	30.73 KB (-0.11% 🔽)
@sentry/react	24.43 KB (-0.09% 🔽)
@sentry/react (incl. Tracing)	35.88 KB (-0.05% 🔽)
@sentry/vue	25.68 KB (-0.18% 🔽)
@sentry/vue (incl. Tracing)	34.7 KB (-0.1% 🔽)
@sentry/svelte	21.88 KB (-0.17% 🔽)
CDN Bundle	24.26 KB (-0.2% 🔽)
CDN Bundle (incl. Tracing)	34.33 KB (-0.09% 🔽)
CDN Bundle (incl. Tracing, Replay)	68.02 KB (-0.05% 🔽)
CDN Bundle (incl. Tracing, Replay, Feedback)	73.01 KB (-0.05% 🔽)
CDN Bundle - uncompressed	71.39 KB (-0.11% 🔽)
CDN Bundle (incl. Tracing) - uncompressed	101.81 KB (-0.08% 🔽)
CDN Bundle (incl. Tracing, Replay) - uncompressed	211.43 KB (-0.04% 🔽)
CDN Bundle (incl. Tracing, Replay, Feedback) - uncompressed	223.79 KB (-0.04% 🔽)
@sentry/nextjs (client)	35.14 KB (-0.1% 🔽)
@sentry/sveltekit (client)	33.48 KB (-0.14% 🔽)
@sentry/node	114.09 KB (+0.01% 🔺)
@sentry/aws-serverless	103 KB (+0.01% 🔺)