Introduce comptime builtins corresponding to FunC string literal types

[anton-trunov]

like h, c, etc. See https://docs.ton.org/develop/func/literals_identifiers.

I don't think we should extend the syntax of string literals with these suffixes, because those are too cryptic for beginners, we should just introduce those as compile-time builtin functions, like crc32("foobar") as a Tact analogue for "foobar"c in FunC.

• "string"s — defines a raw slice const by its contents (hex-encoded and optionally bit-padded) [added in PR #787 - rawSlice("string")];
• "string"a — creates a slice const containing MsgAddressInt structure from a specified address [already have it: address("string")];
• "string"u — creates an int const that corresponds to the hex values of the provided ASCII string [added in PR #787 - ascii("string")];
• "string"h — creates an int const that is the first 32 bits of the SHA256 hash of the string [no need: can be solved with sha256 and a bit mask, this will be optimized in compile-time];
• "string"H — creates an int const that is all 256 bits of the SHA256 hash of the string [already have it: sha256("string")];
• "string"c — creates an int const that is crc32 value of the string [added in PR #787: crc32("string")].

[Gusarich]

• "string"a — creates a slice const containing MsgAddressInt structure from a specified address;

this one is an already existing address()