Make tokenize CLI tool have nicer command line arguments. (#6188)

Make tokenize CLI tool have nicer command line arguments. (#6188)

* Make tokenizer.cpp CLI tool nicer.

Before this commit, tokenize was a simple CLI tool like this:

  tokenize MODEL_FILENAME PROMPT [--ids]

This simple tool loads the model, takes the prompt, and shows the tokens
llama.cpp is interpreting.

This changeset makes the tokenize more sophisticated, and more useful
for debugging and troubleshooting:

  tokenize [-m, --model MODEL_FILENAME]
           [--ids]
           [--stdin]
           [--prompt]
           [-f, --file]
           [--no-bos]
           [--log-disable]

It also behaves nicer on Windows now, interpreting and rendering Unicode
from command line arguments and pipes no matter what code page the user
has set on their terminal.

* style fix: strlen(str) == 0 --> *str == 0

* Simplify tokenize.cpp; by getting rid of handling positional style arguments.

It must now be invoked with long --model, --prompt etc. arguments only.
Shortens the code.

* tokenize.cpp: iostream header no longer required

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Co-authored-by: Georgi Gerganov <redacted>
Co-authored-by: brian khuu <redacted>