patch 8.2.0578: heredoc for interfaces does not support "trim"

Problem:    Heredoc for interfaces does not support "trim".
Solution:   Update the script heredoc support to be same as the :let command.
            (Yegappan Lakshmanan, closes #5916)
diff --git a/runtime/doc/if_lua.txt b/runtime/doc/if_lua.txt
index ad20b01..75bb963 100644
--- a/runtime/doc/if_lua.txt
+++ b/runtime/doc/if_lua.txt
@@ -32,7 +32,7 @@
 	:lua local curbuf = vim.buffer() curbuf[7] = "line #7"
 <
 
-:[range]lua << [endmarker]
+:[range]lua << [trim] [{endmarker}]
 {script}
 {endmarker}
 			Execute Lua script {script}.
@@ -40,10 +40,9 @@
 			feature wasn't compiled in.  To avoid errors, see
 			|script-here|.
 
-The {endmarker} must NOT be preceded by any white space.
-
 If [endmarker] is omitted from after the "<<", a dot '.' must be used after
-{script}, like for the |:append| and |:insert| commands.
+{script}, like for the |:append| and |:insert| commands.  Refer to
+|:let-heredoc| for more information.
 
 This form of the |:lua| command is mainly useful for including Lua code
 in Vim scripts.
diff --git a/runtime/doc/if_mzsch.txt b/runtime/doc/if_mzsch.txt
index da43829..6420856 100644
--- a/runtime/doc/if_mzsch.txt
+++ b/runtime/doc/if_mzsch.txt
@@ -39,7 +39,7 @@
 :[range]mz[scheme] {stmt}
 			Execute MzScheme statement {stmt}.
 
-:[range]mz[scheme] << [endmarker]
+:[range]mz[scheme] << [trim] [{endmarker}]
 {script}
 {endmarker}
 			Execute inlined MzScheme script {script}.
@@ -47,12 +47,11 @@
 			feature wasn't compiled in.  To avoid errors, see
 			|script-here|.
 
-			The {endmarker} below the {script} must NOT be
-			preceded by any white space.
-
 			If [endmarker] is omitted from after the "<<", a dot
 			'.' must be used after {script}, like for the
-			|:append| and |:insert| commands.
+			|:append| and |:insert| commands.  Refer to
+			|:let-heredoc| for more information.
+
 
 							*:mzfile* *:mzf*
 :[range]mzf[ile] {file}	Execute the MzScheme script in {file}.
diff --git a/runtime/doc/if_perl.txt b/runtime/doc/if_perl.txt
index f1bf923..b0bad1e 100644
--- a/runtime/doc/if_perl.txt
+++ b/runtime/doc/if_perl.txt
@@ -55,7 +55,7 @@
 			working: >
 				:perl VIM::Msg("Hello")
 
-:pe[rl] << [endmarker]
+:pe[rl] << [trim] [{endmarker}]
 {script}
 {endmarker}
 			Execute Perl script {script}.
diff --git a/runtime/doc/if_pyth.txt b/runtime/doc/if_pyth.txt
index 88e0df6..572e6bf 100644
--- a/runtime/doc/if_pyth.txt
+++ b/runtime/doc/if_pyth.txt
@@ -34,7 +34,7 @@
 			the `:python` command is working: >
 				:python print "Hello"
 
-:[range]py[thon] << [endmarker]
+:[range]py[thon] << [trim] [{endmarker}]
 {script}
 {endmarker}
 			Execute Python script {script}.
@@ -42,10 +42,9 @@
 			feature wasn't compiled in.  To avoid errors, see
 			|script-here|.
 
-The {endmarker} below the {script} must NOT be preceded by any white space.
-
 If [endmarker] is omitted from after the "<<", a dot '.' must be used after
-{script}, like for the |:append| and |:insert| commands.
+{script}, like for the |:append| and |:insert| commands.  Refer to
+|:let-heredoc| for more information.
 
 This form of the |:python| command is mainly useful for including python code
 in Vim scripts.
@@ -768,12 +767,12 @@
 
 							*:py3* *:python3*
 :[range]py3 {stmt}
-:[range]py3 << [endmarker]
+:[range]py3 << [trim] [{endmarker}]
 {script}
 {endmarker}
 
 :[range]python3 {stmt}
-:[range]python3 << [endmarker]
+:[range]python3 << [trim] [{endmarker}]
 {script}
 {endmarker}
 	The `:py3` and `:python3` commands work similar to `:python`.  A
diff --git a/runtime/doc/if_ruby.txt b/runtime/doc/if_ruby.txt
index 4523660..dc8349f 100644
--- a/runtime/doc/if_ruby.txt
+++ b/runtime/doc/if_ruby.txt
@@ -28,15 +28,15 @@
 :rub[y] {cmd}		Execute Ruby command {cmd}.  A command to try it out: >
 				:ruby print "Hello"
 
-:rub[y] << [endmarker]
+:rub[y] << [trim] [{endmarker}]
 {script}
 {endmarker}
 			Execute Ruby script {script}.
-			The {endmarker} after {script} must NOT be preceded by
-			any white space.
 
 			If [endmarker] is omitted, it defaults to a dot '.'
-			like for the |:append| and |:insert| commands.
+			like for the |:append| and |:insert| commands.  Refer
+			to |:let-heredoc| for more information.
+
 
 			This form of the |:ruby| command is mainly useful for
 			including ruby code in vim scripts.
diff --git a/runtime/doc/if_tcl.txt b/runtime/doc/if_tcl.txt
index f7c0d6f..60ac6bc 100644
--- a/runtime/doc/if_tcl.txt
+++ b/runtime/doc/if_tcl.txt
@@ -30,7 +30,7 @@
 			is working: >
 				:tcl puts "Hello"
 
-:[range]tc[l] << [endmarker]
+:[range]tc[l] << [trim] [{endmarker}]
 {script}
 {endmarker}
 			Execute Tcl script {script}.
@@ -38,10 +38,9 @@
 			wasn't compiled in.  To avoid errors, see
 			|script-here|.
 
-The {endmarker} after {script} must NOT be preceded by any white space.
-
 If [endmarker] is omitted from after the "<<", a dot '.' must be used after
-{script}, like for the |:append| and |:insert| commands.
+{script}, like for the |:append| and |:insert| commands.  Refer to
+|:let-heredoc| for more information.
 
 This form of the |:tcl| command is mainly useful for including tcl code in Vim
 scripts.