Implement translated template string formatting in Rust

[obrusvit]

Moving forward, we'd like to have the capability to format translation strings directly in Rust and we don't want to count on MicroPython and pass pre-formatted strings to Rust layouts.

Currently, we have to do something like this (not real code):

text = TR.reset__words_written_down_template.format(words_count)
layout = trezorui_api.show_share_words_mercury(words, text=text)

If the text is not influenced by uPy app, we should be able to pass just words to Rust and format the text there.

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What we can do right now is to format using uformat! from ufmt crate, but the drawback is that the format string can only be a string literal:

uformat!("{}. {}", self.page_index + 1, w)

I.e. something like this is not possible using ufmt:

// reset__word_x_of_y: "Word {0} of {1}"
uformat!(TR::reset__word_x_of_y, n, words.len())

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The task is to find, test, integrate and review an external crate which can do that, or develop our own.