Problem: Vim9: runtime and compile time type checks are not the same.
Solution: Add more runtime type checks for builtin functions. (Yegappan
Lakshmanan, closes#8646)
Problem: Vim9: argument types are not checked at compile time.
Solution: Add several more type checks, also at runtime. (Yegappan
Lakshmanan, closes#8587)
Problem: Vim9: leaking memory when using continuation line.
Solution: Keep a pointer to the continuation line in evalarg_T. Centralize
checking for a next command.
