completion: use awk for filtering the config entries

Commits 1e0ee40 (completion: add and use
__git_compute_first_level_config_vars_for_section, 2024-02-10) and
6e32f71 (completion: add and use
__git_compute_second_level_config_vars_for_section, 2024-02-10)
introduced new helpers for config completion.

Both helpers use a pipeline of grep and awk to filter the list of config
entries. awk is perfectly capable of filtering, so let's eliminate the
grep process and move the filtering into the awk script.

The "-E" grep option (extended syntax) was not necessary, as $section is
a single word.

While at it, wrap the over-long lines to make them more readable.

Signed-off-by: Beat Bolli <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: bbolli

contrib/completion/git-completion.bash

@@ -2673,7 +2673,8 @@ __git_compute_first_level_config_vars_for_section ()
 	__git_compute_config_vars
 	local this_section="__git_first_level_config_vars_for_section_${section}"
 	test -n "${!this_section}" ||
-	printf -v "__git_first_level_config_vars_for_section_${section}" %s "$(echo "$__git_config_vars" | grep -E "^${section}\.[a-z]" | awk -F. '{print $2}')"
+	printf -v "__git_first_level_config_vars_for_section_${section}" %s \
+		"$(echo "$__git_config_vars" | awk -F. "/^${section}\.[a-z]/ { print \$2 }")"
 }
 
 __git_compute_second_level_config_vars_for_section ()
@@ -2682,7 +2683,8 @@ __git_compute_second_level_config_vars_for_section ()
 	__git_compute_config_vars_all
 	local this_section="__git_second_level_config_vars_for_section_${section}"
 	test -n "${!this_section}" ||
-	printf -v "__git_second_level_config_vars_for_section_${section}" %s "$(echo "$__git_config_vars_all" | grep -E "^${section}\.<" | awk -F. '{print $3}')"
+	printf -v "__git_second_level_config_vars_for_section_${section}" %s \
+		"$(echo "$__git_config_vars_all" | awk -F. "/^${section}\.</ { print \$3 }")"
 }
 
 __git_config_sections=