fix: improve funcId recognition and squash misdetection bugs

[novusnota]

That took a looooooooot of RegEx iterations.

Closes #635

• I have updated CHANGELOG.md
  - [ ] I have documented my contribution in Tact Docs: https://github.com/tact-lang/tact-docs/pull/PR-NUMBER
• I have added tests to demonstrate the contribution is correctly implemented: this usually includes both positive and negative tests, showing the happy path(s) and featuring intentionally broken cases
• I have run all the tests locally and no test failure was reported
• I have run the linter, formatter and spellchecker
• I did not do unrelated and/or undiscussed refactorings

[anton-trunov]

To be on the safe side, let's take stdlib.fc and mathlib.fc as libraries that are commonly used and see if we can add more function identifiers from those libs into our positive tests to make sure people will be able to FFI with those.

[anton-trunov]

This PR accepts, for instance, + as a valid FunC identifier, but it's actually not.

Something like this should work:

    funcInvalidId = "_" ")" --notUnderscore
                  | ("+" | "-" | "*" | "/" | "~/" | "^/" | "%" | "~%" | "^%" | "/%") ")" --notArithOperator
      // more operators here
                  | ("-"? digit+) ")" --notDecimalNumber
                  | ("-"? "0x" hexDigit+) ")" --notHexadecimalNumber
    funcPlainId = ~funcInvalidId (~(whiteSpace | "(" | ")" | "," | "." | ";" | "~") any)+

[novusnota]

Nice observation! I'd try putting lookaheads & in front of those ")" so they don't get parsed, but let me try your suggestion first, it should work. UPD: Yeah, it does, clever idea!

The keywords are not allowed and should be excluded too. Basically, contents of https://github.com/ton-blockchain/ton/blob/master/crypto/func/keywords.cpp has to be put in the exceptions list. I'm on it.

UPD2: Order of operators in those inner () alternations really does matter, the ones with bigger prefix shall stand in front of others.

[novusnota]

There was a suggestion, which didn't pass negative tests, so I hid it.

The thing we've engineered works, but possibly I've found a cleaner solution, which doesn't require the ")" and can be used in the FunC parser too (the current approach in this PR fails there in absence of ")" and stuff). But this one works:

It passes similar set of tests we have for function identifiers, but adapted to FunC code:

UPD: Negative tests failed terribly, reverting :)

[anton-trunov]

@novusnota So, what's the current status of this PR?

[novusnota]

@anton-trunov It's a working and robust solution. The alternative would be to do invalidation of identifiers during syntactic analysis, which enhances the error messages further, but that seems to be a bit out of scope of this PR. Wdyt?