[7.x] [data][bfetch] Avoid using Buffer in client code (#107278)

[kibanamachine]

Backports the following commits to 7.x:

• [data][bfetch] Avoid using Buffer in client code ([data][bfetch] Avoid using Buffer in client code #107278)

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: c97e642
• Storybooks Preview

Metrics [docs]

Module Count

Fewer modules leads to a faster build time

id	before	after	diff
bfetch	29	25	-4
data	616	597	-19
total			-23

Page load bundle

Size of the bundles that are downloaded on every page load. Target size is below 100kb

id	before	after	diff
bfetch	46.9KB	16.0KB	-30.9KB
data	909.4KB	873.1KB	-36.3KB
total			-67.3KB

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

cc @Dosant