Fix styling of Unicode codepoints in manuals

* doc/lispref/nonascii.texi (Character Properties):
* doc/lispref/display.texi (Glyphless Chars)
(Bidirectional Display):
* doc/emacs/search.texi (Lax Search):
* doc/emacs/text.texi (Quotation Marks):
* doc/emacs/basic.texi (Inserting Text): Canonicalize the
style of "U+NNNN CHARACTER NAME".  (Bug#35885)
1 job for emacs-26 in 6 seconds (queued for 5 seconds)
Status Job ID Name Coverage
failed #2014


Name Stage Failure
test Test There has been a runner system failure, please try again
Running with gitlab-runner 11.6.0 (f100a208)
on gitlab-runner-docker cff9d373
Using Docker executor with image debian:stretch ...
Pulling docker image debian:stretch ...
Using docker image sha256:8d31923452f8b79ae91b01568d28c90e7d667a9eaff9734c6faeb017b0efa8d0 for debian:stretch ...
ERROR: Job failed (system failure): Error response from daemon: failed to start shim: exec: "docker-containerd-shim": executable file not found in $PATH: unknown (executor_docker.go:1018:1s)