patch 8.2.4603: sourcing buffer lines is too complicated

Problem:    Sourcing buffer lines is too complicated.
Solution:   Simplify the code. Make it possible to source Vim9 script lines.
            (Yegappan Lakshmanan, closes #9974)
diff --git a/runtime/doc/repeat.txt b/runtime/doc/repeat.txt
index a775af0..f7756c1 100644
--- a/runtime/doc/repeat.txt
+++ b/runtime/doc/repeat.txt
@@ -201,7 +201,13 @@
 :[range]so[urce] 	Read Ex commands from the [range] of lines in the
 			current buffer.  When sourcing commands from the
 			current buffer, the same script-ID |<SID>| is used
-			even if the buffer is sourced multiple times.
+			even if the buffer is sourced multiple times. If a
+			buffer is sourced more than once, then the functions
+			in the buffer are redefined again.
+			Sourcing a buffer with a Vim9 script more than once
+			works like |vim9-reload|.
+			To source a script in the Vim9 context, the |:vim9cmd|
+			modifier can be used.
 
 							*:source!*
 :so[urce]! {file}	Read Vim commands from {file}.  These are commands
@@ -425,10 +431,10 @@
 ':source!' command.  Useful for long command sequences.  Can be combined with
 the ':map' command to put complicated commands under a function key.
 
-The ':source' command reads Ex commands from a file line by line.  You will
-have to type any needed keyboard input.  The ':source!' command reads from a
-script file character by character, interpreting each character as if you
-typed it.
+The ':source' command reads Ex commands from a file or a buffer line by line.
+You will have to type any needed keyboard input.  The ':source!' command reads
+from a script file character by character, interpreting each character as if
+you typed it.
 
 Example: When you give the ":!ls" command you get the |hit-enter| prompt.  If
 you ':source' a file with the line "!ls" in it, you will have to type the