feat(edit): insert an unsimplified key using CTRL-SHIFT-V

This marks the following Vim patches as ported:

vim-patch:8.1.2333: with modifyOtherKeys CTRL-^ doesn't work

Problem:    With modifyOtherKeys CTRL-^ doesn't work.
Solution:   Handle the exception.
https://github.com/vim/vim/commit/828ffd596394f714270a01a55fc3f949a8bd9b35

vim-patch:8.1.2350: other text for CTRL-V in Insert mode with modifyOtherKeys

Problem:    Other text for CTRL-V in Insert mode with modifyOtherKeys.
Solution:   Convert the Escape sequence back to key as if modifyOtherKeys is
            not set, and use CTRL-SHIFT-V to get the Escape sequence itself.
            (closes vim/vim#5254)
https://github.com/vim/vim/commit/fc4ea2a72d36de1196a3ce17352e72f8fe90f4bb

vim-patch:8.2.2084: CTRL-V U doesn't work to enter a Unicode character

Problem:    CTRL-V U doesn't work to enter a Unicode character when
            modifyOtherKeys is effective. (Ken Takata)
Solution:   Add a flag to get_literal() for the shift key. (closes vim/vim#7413)
https://github.com/vim/vim/commit/0684e36a7ee0743f2889698fb8e0e14f7acae423

Omit getcmdkeycmd() change as it depends on Vim patch 8.2.2062, which
may introduce a potential breakage.

2 files changed, 16 insertions, 3 deletions

diff --git a/runtime/doc/cmdline.txt b/runtime/doc/cmdline.txt
index 9fa2034718..6228c9238f 100644
--- a/runtime/doc/cmdline.txt
+++ b/runtime/doc/cmdline.txt
@@ -67,12 +67,19 @@ CTRL-V		Insert next non-digit literally.  Up to three digits form the
 		decimal value of a single byte.  The non-digit and the three
 		digits are not considered for mapping.  This works the same
 		way as in Insert mode (see above, |i_CTRL-V|).
+		For special keys, the CTRL modifier may be included into the
+		key to produce a control character.  If there is no control
+		character for the key then its |key-notation| is inserted.
 		Note: Under Windows CTRL-V is often mapped to paste text.
 		Use CTRL-Q instead then.
 							*c_CTRL-Q*
 CTRL-Q		Same as CTRL-V.  But with some terminals it is used for
 		control flow, it doesn't work then.
 
+CTRL-SHIFT-V				*c_CTRL-SHIFT-V* *c_CTRL-SHIFT-Q*
+CTRL-SHIFT-Q	Works just like CTRL-V, but do not try to include the CTRL
+		modifier into the key.
+
 							*c_<Left>* *c_Left*
 <Left>		cursor left
 							*c_<Right>* *c_Right*
diff --git a/runtime/doc/insert.txt b/runtime/doc/insert.txt
index 9db44eaaa0..7f6662089d 100644
--- a/runtime/doc/insert.txt
+++ b/runtime/doc/insert.txt
@@ -192,12 +192,14 @@ CTRL-D		Delete one shiftwidth of indent at the start of the current
 		label.
 
 						*i_CTRL-V*
-CTRL-V		Insert next non-digit literally.  For special keys, the
-		terminal code is inserted.  It's also possible to enter the
-		decimal, octal or hexadecimal value of a character
+CTRL-V		Insert next non-digit literally.  It's also possible to enter
+		the decimal, octal or hexadecimal value of a character
 		|i_CTRL-V_digit|.
 		The characters typed right after CTRL-V are not considered for
 		mapping.
+		For special keys, the CTRL modifier may be included into the
+		key to produce a control character.  If there is no control
+		character for the key then its |key-notation| is inserted.
 		Note: When CTRL-V is mapped (e.g., to paste text) you can
 		often use CTRL-Q instead |i_CTRL-Q|.
 
@@ -206,6 +208,10 @@ CTRL-Q		Same as CTRL-V.
 		Note: Some terminal connections may eat CTRL-Q, it doesn't
 		work then.  It does work in the GUI.
 
+CTRL-SHIFT-V				*i_CTRL-SHIFT-V* *i_CTRL-SHIFT-Q*
+CTRL-SHIFT-Q	Works just like CTRL-V, but do not try to include the CTRL
+		modifier into the key.
+
 CTRL-X		Enter CTRL-X mode.  This is a sub-mode where commands can
 		be given to complete words or scroll the window.  See
 		|i_CTRL-X| and |ins-completion|.