ci: update all library READMES with a single script (#7695)

Use some markers in each library `README.md` file to inject the
`quickstart.cc` code. With this change it is now possible to update all
the libraries using a single script.

I also changed the scaffold generation to include these markers for
future libraries.

ci/cloudbuild/builds/checkers.sh

@@ -19,6 +19,7 @@ set -euo pipefail
 source "$(dirname "$0")/../../lib/init.sh"
 source module ci/lib/io.sh
 source module ci/cloudbuild/builds/lib/git.sh
+source module ci/cloudbuild/builds/lib/features.sh
 
 # Runs sed expressions (specified after -e) over the given files, editing them
 # in place. This function is exported so it can be run in subshells, such as
@@ -82,17 +83,16 @@ printf "%-30s" "Running markdown generators:" >&2
 time {
   declare -A -r GENERATOR_MAP=(
     ["ci/generate-markdown/generate-readme.sh"]="README.md"
-    ["ci/generate-markdown/generate-bigquery-readme.sh"]="google/cloud/bigquery/README.md"
-    ["ci/generate-markdown/generate-bigtable-readme.sh"]="google/cloud/bigtable/README.md"
-    ["ci/generate-markdown/generate-iam-readme.sh"]="google/cloud/iam/README.md"
-    ["ci/generate-markdown/generate-pubsub-readme.sh"]="google/cloud/pubsub/README.md"
-    ["ci/generate-markdown/generate-spanner-readme.sh"]="google/cloud/spanner/README.md"
-    ["ci/generate-markdown/generate-storage-readme.sh"]="google/cloud/storage/README.md"
     ["ci/generate-markdown/generate-packaging.sh"]="doc/packaging.md"
   )
   for generator in "${!GENERATOR_MAP[@]}"; do
     "${generator}" >"${GENERATOR_MAP[${generator}]}"
   done
+
+  mapfile -t libraries < <(features::libraries)
+  for library in "${libraries[@]}"; do
+    ci/generate-markdown/update-library-readme.sh "${library}"
+  done
 }
 
 printf "%-30s" "Running check-include-guards:" >&2

ci/cloudbuild/builds/lib/features.sh

@@ -22,15 +22,24 @@ if ((CI_CLOUDBUILD_BUILDS_LIB_FEATURES_SH__++ != 0)); then
   return 0
 fi # include guard
 
-function features::list() {
+function features::libraries() {
   local feature_list
-  mapfile -t feature_list < <(cat ci/etc/full_feature_list)
-  # Add the hand-crafted libraries and custom features to the full list
+  mapfile -t feature_list <ci/etc/full_feature_list
+  # Add the hand-crafted libraries
   feature_list+=(
     bigtable
     pubsub
     spanner
     storage
+  )
+  printf "%s\n" "${feature_list[@]}"
+}
+
+function features::list() {
+  local feature_list
+  mapfile -t feature_list < <(features::libraries)
+  # Add any custom features to the full list of libraries
+  feature_list+=(
     experimental-storage-grpc
   )
   printf "%s\n" "${feature_list[@]}"