patch 9.1.1169: using global variable for get_insert()/get_lambda_name()

Problem:  using global variable for get_insert()/get_lambda_name()
          (after v9.1.1151)
Solution: let the functions return a string_T object instead
          (Yee Cheng Chin)

In #16720, `get_insert()` was modified to store a string length in a
global variable to be queried immediately by another `get_insert_len()`
function, which is somewhat fragile. Instead, just have the function
itself return a `string_T` object instead. Also do the same for
`get_lambda_name()` which has similar issues.

closes: #16775

Signed-off-by: Yee Cheng Chin <ychin.git@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/proto/getchar.pro b/src/proto/getchar.pro
index c1eb1ab..11a37fb 100644
--- a/src/proto/getchar.pro
+++ b/src/proto/getchar.pro
@@ -1,7 +1,6 @@
 /* getchar.c */
 char_u *get_recorded(void);
-char_u *get_inserted(void);
-size_t get_inserted_len(void);
+string_T get_inserted(void);
 int stuff_empty(void);
 int readbuf1_empty(void);
 void typeahead_noflush(int c);