Backport 'read -a' and 'read -p' from ksh 93v-/2020

This backports two minor additions to the 'read' built-in from ksh
93v-: '-a' is now the same as '-A' and '-u p' is the same as '-p'.
This is for compatibility with some 93v- or ksh2020 scripts.

Note that their change to the '-p' option to support both prompts
and reading from the coprocess was *not* backported because we
found it to be broken and unfixable. Discussoin at:
https://github.com/ksh93/ksh/issues/463

src/cmd/ksh93/bltins/read.c: b_read():
- Backport as described above.
- Rename the misleadingly named 'name' variable to 'prompt'.
  It points to the prompt string, not to a variable name.

src/cmd/ksh93/data/builtins.c: sh_optpwd[]:
- Add -a as an alterative to -A. All that is needed is adding '|a'
  and optget(3) will automatically convert it to 'A'.
- Change -u from a '#' (numeric) to ':' option to support 'p'. Note
  that b_read() now needs a corresponding strtol() to convert file
  descriptor strings to numbers where applicable.
- Tweaks.

src/cmd/ksh93/sh.1:
- Update accordingly.
- Tidy up the unreadable mess that was the 'read' documentation.
  The options are now shown in a list.

NEWS

@@ -3,6 +3,14 @@ For full details, see the git log at: https://github.com/ksh93/ksh/tree/1.0
 
 Any uppercase BUG_* names are modernish shell bug IDs.
 
+2022-01-16:
+
+- Backported minor additions to the 'read' built-in command from ksh 93v-:
+  '-a' is now the same as '-A' and '-u p' is the same as '-p'. This is for
+  compatibility with some 93v- or ksh2020 scripts. (Note that their change
+  to the '-p' option to support both prompts and coprocess reads was not
+  backported because we found it to be broken and unfixable.)
+
 2022-02-15:
 
 - A bug was fixed in fast filescan loops (like 'while <file; do ...; done',