Anchor links are not reliable in YARD

...so we should avoid them and describe anchor positions with English.
Use indented code blocks instead of fenced ones

Our docs toolchain can't handle fenced code blocks yet, and we're going to need
to put this content in multiple places, so it must use least-common-denominator
markdown syntax.
Rename files (and any references to them)

Underscores are nicer than camels.
Title-case the headers
Modify the manifest to not throw an error; add node definitions
Add explanatory text
Merge remote-tracking branch 'nfagerlund/rest_yard' into issue/21881-document-resource-type

* nfagerlund/rest_yard:
  Add explanatory text
  Modify the manifest to not throw an error; add node definitions
  Title-case the headers
  Rename files (and any references to them)
  Use indented code blocks instead of fenced ones
  Anchor links are not reliable in YARD