Support integer literals of different radices and decimal numeric literals

[chengluyu]

This PR adds the support for various literals.

• Hexadecimal integer literals: 0xCAFE, etc.
• Octal integer literals: 0o4567, etc.
• Binary integer literals: 0b0010, etc.
• Decimal numeric literals in floating-point style: 1e100, 3.141592653589793, etc.
• Support separators to be interleaved in all digits: 0x0010_1101, 12_34.56_78E+9_0, etc.
• Lastly, the support for string escapes \\, \b, and \f. (I forgot this so it's not indicated by my commit messages. 🤦‍♂️)

[!NOTE]
This PR does not support numeric literals starting with decimal points, for example, .5, because it conflicts with selecting tuple indices. We can check the accumulated tokens to determine the meaning of tokens such as .1, but I don't have time to summarize various situations and add tests right now, so I will leave it for future work.

[chengluyu]

6182f20 failed for some reasons. Strange.

[NeilKleistGao]

6182f20 failed for some reasons. Strange.

Random-happened time-out problem lol.