[token-cli] Remove is_amount_or_all, is_amount, and is_parsable validators

[samkim-crypto]

Problem

The token-cli now uses clap-v3, but there are still some deprecated functions that should be removed (we ultimately want to remove #![allow(deprecated)] at the top of clap_app.rs). In particular, with clap-v3, input validation has been deprecated in favor of just parsing the inputs.

All of the occurrences of Arg::validator in the token-cli should be replaced with Arg::value_parser. Since there are many of these occurrences, I think these can be removed in a sequence of smaller PRs.

Summary of Changes

In this PR, I started removing validator functions related to numbers and amounts. I think the changes should be pretty straightforward:

318244b: I started with removing validator is_mint_decimals from the clap app and replacing it with the clap builtin parser clap::value_parser!(u8) instead. When actually parsing the inputs, we either used the deprecated value_t_or_exit or parsed the input as a string and converted it to u8. I now updated it to directly use get_one::<u8>("decimals") instead.

eff3494: For arguments related to token amount, we used the is_amount_or_all validator that checks whether it is an unsigned integer (u64), decimals (f64), or the All keyword. In clap-v3, the Amount type was added to parse these type of arguments, so I used Amount::parse to replace is_amount_or_all. When actually parsing the inputs, I had to use match statements, which makes things a little bit more verbose, but I think the code itself should be a lot more readable.

06b0c1f: For the arguments, we use the is_amount validator function as well, which can either be an unsigned integer (u64) or decimals (f64) (but not All keyword). I replaced these with either Amount::parse or clap::value_parser!(u64) whichever made sense. In the process, I noticed that we had some inconsistency in the way we name the argument for maximum fee. We sometimes use MAXIMUM_FEE and sometimes use TOKEN_AMOUNT. I ended up fixing this to all use MAXIMUM_FEE instead for consistency. This renaming should just be a cosmetic change.

ac50d8f: Finally, there were occurrences of validator is_parsable::<TYPE>. I replaced these with direct clap parsers clap::value_parser!(TYPE).

There are other validator functions like is_valid_signer and is_valid_pubkey that we use throughout the code. These will be removed in follow-up PRs.