patch 8.2.4883: string interpolation only works in heredoc
Problem: String interpolation only works in heredoc.
Solution: Support interpolated strings. Use syntax for heredoc consistent
with strings, similar to C#. (closes #10327)
diff --git a/src/proto/typval.pro b/src/proto/typval.pro
index 459cf7c..5b1f974 100644
--- a/src/proto/typval.pro
+++ b/src/proto/typval.pro
@@ -72,6 +72,7 @@
int eval_lit_string(char_u **arg, typval_T *rettv, int evaluate);
char_u *tv2string(typval_T *tv, char_u **tofree, char_u *numbuf, int copyID);
int eval_env_var(char_u **arg, typval_T *rettv, int evaluate);
+int eval_interp_string(char_u **arg, typval_T *rettv, int evaluate);
linenr_T tv_get_lnum(typval_T *argvars);
linenr_T tv_get_lnum_buf(typval_T *argvars, buf_T *buf);
buf_T *tv_get_buf(typval_T *tv, int curtab_only);