(FunC) Add description of multiline strings

[novusnota]

Is your feature request related to a problem? Please describe.

In https://docs.ton.org/develop/func/literals_identifiers#string-literals, it's stated that there are no multiline strings, which isn't true — all the same multiline strings from multiline assembly function definitions can be used in expressions. And they also have all the same "string types": s for slices of hex-encoded string contents, a for slices containing MsgAddressInt of address in string contents, etc.

The following just works:

;; somewhere inside of a function body

var a = """
   hash me baby one more time
"""h;
var b = a + 42;

b; ;; 623173419

Describe the solution you'd like

Add description of multiline string literals :)

Additional context

While we're at it — Did you know, that Fift assembly function bodies can have sequences of both singleline and multiline string literals mixed? That is, the following is perfectly valid:

int inc_negate_inc(int x) asm "INC" """
    NEGATE
""" "INC";

...which would increment the value on the stack by 1, negate it, then increment by 1 again and pop it, producing it as a result.