Document mutability for built-ins

Suggested in https://github.com/argotorg/solidity/pull/15968#discussion_r2718881831

Currently, in [cheatsheet section](https://docs.soliditylang.org/en/latest/cheatsheet.html) of the docs, built-ins don't have their mutability explicitly stated.
For example:
```solidity
erc7201(string memory id) returns (uint)
```
should be
```solidity
erc7201(string memory id) pure returns (uint)
```

It should also be noted the distinction between built-ins which are usable in compile time (e.g., usable in layouts and array sizing) or runtime constant (usable in `constant` initializers).

Start with the cheatsheet section in docs.soliditylang.org/en/latest/cheatsheet.html and review the discussion in pull request 15968. Document mutability for each built-in and distinguish compile-time usability from runtime constants; the cheatsheet should clearly show these properties for the listed built-ins.

Written by the indexing model from the issue text.