SendParameters Sanity Checker

[jubnzv]

Summary
Check dangerous patterns in the mode field of SendParameters.

Context
tact-lang/tact#180

Examples

SendParameters{
    ...
    mode: SendRemainingValue + SendRemainingValue, 
    ...
}

Should raise a warning:

• flags in the mode field should be used at most one time;
• the mode expression should only contain the + sign;
• TODO: check if some combinations of flags are meaningless;
• integer literals should not be used, only symbolic constants.

[jubnzv]

Additional idea: maybe we could leverage the Tact interpreter to reason about possible problems of mode values (depends on #70)

[Gusarich]

• the mode expression should only contain the + sign;

actually it's recommended to use the binary or | operator instead of +:
tact-lang/tact#180 (comment)