[bash-completion] Optimize __fzf_orig_completion_filter

Commit d4ad4a2 slowed loading of completion.bash significantly (on my
laptop from 10 ms to 30 ms), then 54891d1 improved that (to 20 ms) but
it still stands out as the heavy part of my .bashrc.

Rewriting __fzf_orig_completion_filter to pure bash without forking to
sed/awk brings this back under 10 ms.

before:

    $ HISTFILE=/tmp/bashhist hyperfine 'bash --rcfile shell/completion.bash -i'
    Benchmark #1: bash --rcfile shell/completion.bash -i
      Time (mean ± σ):      21.2 ms ±   0.3 ms    [User: 24.9 ms, System: 6.4 ms]
      Range (min … max):    20.7 ms …  23.3 ms    132 runs

after:

    $ HISTFILE=/tmp/bashhist hyperfine 'bash --rcfile shell/completion.bash -i'
    Benchmark #1: bash --rcfile shell/completion.bash -i
      Time (mean ± σ):       9.6 ms ±   0.3 ms    [User: 8.0 ms, System: 2.2 ms]
      Range (min … max):     9.3 ms …  11.4 ms    298 runs

Fixes: d4ad4a2 ("[bash-completion] Fix default alias/variable completion")
Fixes: 54891d1 ("[bash-completion] Minor optimization")

shell/completion.bash

@@ -46,9 +46,19 @@ __fzf_comprun() {
   fi
 }
 
-__fzf_orig_completion_filter() {
-  sed '/ -F/!d; / _fzf/d; s/^\(.*-F\) *\([^ ]*\).* \([^ ]*\)$/export _fzf_orig_completion_\3="\1 %s \3 #\2"; [[ "\1" = *" -o nospace "* ]] \&\& [[ ! "$__fzf_nospace_commands" = *" \3 "* ]] \&\& __fzf_nospace_commands="$__fzf_nospace_commands \3 ";/' |
-  awk -F= '{OFS = FS} {gsub(/[^A-Za-z0-9_= ;]/, "_", $1);}1'
+__fzf_orig_completion() {
+  local l comp f cmd
+  while read -r l; do
+    if [[ "$l" =~ ^(.*\ -F)\ *([^ ]*).*\ ([^ ]*)$ ]]; then
+      comp="${BASH_REMATCH[1]}"
+      f="${BASH_REMATCH[2]}"
+      cmd="${BASH_REMATCH[3]}"
+      export "_fzf_orig_completion_${cmd//[^A-Za-z0-9_]/_}=${comp} %s ${cmd} #${f}"
+      if [[ "$l" = *" -o nospace "* ]] && [[ ! "$__fzf_nospace_commands" = *" $cmd "* ]]; then
+        __fzf_nospace_commands="$__fzf_nospace_commands $cmd "
+      fi
+    fi
+  done
 }
 
 _fzf_opts_completion() {
@@ -137,7 +147,7 @@ _fzf_handle_dynamic_completion() {
     ret=$?
     # _completion_loader may not have updated completion for the command
     if [ "$(complete -p "$orig_cmd" 2> /dev/null)" != "$orig_complete" ]; then
-      eval "$(complete | command grep " -F.* $orig_cmd$" | __fzf_orig_completion_filter)"
+      __fzf_orig_completion < <(complete -p "$orig_cmd" 2> /dev/null)
       if [[ "$__fzf_nospace_commands" = *" $orig_cmd "* ]]; then
         eval "${orig_complete/ -F / -o nospace -F }"
       else
@@ -306,9 +316,7 @@ a_cmds="
   svn tar unzip zip"
 
 # Preserve existing completion
-eval "$(complete |
-  sed -E "/ ($(echo $d_cmds $a_cmds | sed 's/ /|/g; s/+/\\+/g'))$/"'!d' |
-  __fzf_orig_completion_filter)"
+__fzf_orig_completion < <(complete -p $d_cmds $a_cmds 2> /dev/null)
 
 if type _completion_loader > /dev/null 2>&1; then
   _fzf_completion_loader=1
@@ -353,7 +361,7 @@ _fzf_setup_completion() {
     return 1
   fi
   shift
-  eval "$(complete -p "$@" 2> /dev/null | __fzf_orig_completion_filter)"
+  __fzf_orig_completion < <(complete -p "$@" 2> /dev/null)
   for cmd in "$@"; do
     case "$kind" in
       dir)   __fzf_defc "$cmd" "$fn" "-o nospace -o dirnames" ;;