patch 8.2.1914: Vim9: cannot put line break in expression for '=' register

Problem:    Vim9: cannot put line break in expression for '=' register.
Solution:   Pass fgetline to set_expr_line(). (closes #7209)
diff --git a/src/proto/eval.pro b/src/proto/eval.pro
index 58ec79c..b1a2c0f 100644
--- a/src/proto/eval.pro
+++ b/src/proto/eval.pro
@@ -11,6 +11,7 @@
 char_u *eval_to_string_skip(char_u *arg, exarg_T *eap, int skip);
 int skip_expr(char_u **pp, evalarg_T *evalarg);
 int skip_expr_concatenate(char_u **arg, char_u **start, char_u **end, evalarg_T *evalarg);
+char_u *eval_to_string_eap(char_u *arg, int convert, exarg_T *eap);
 char_u *eval_to_string(char_u *arg, int convert);
 char_u *eval_to_string_safe(char_u *arg, int use_sandbox);
 varnumber_T eval_to_number(char_u *expr);