Use `String::with_capacity` in `format!`
Add an `Arguments::estimated_capacity` to estimate the length of formatted text and use it in `std::fmt::format` as the initial capacity of the buffer.
The capacity is calculated based on the literal parts of format string, see the details in the implementation.
Some benches:
```rust
empty: format!("{}", black_box(""))
literal: format!("Literal")
long: format!("Hello Hello Hello Hello, {}!", black_box("world"))
long_rev: format!("{}, hello hello hello hello!", black_box("world"))
long_rev_2: format!("{}{}, hello hello hello hello!", 1, black_box("world"))
short: format!("Hello, {}!", black_box("world"))
short_rev: format!("{}, hello!", black_box("world"))
short_rev_2: format!("{}{}, hello!", 1, black_box("world"))
surround: format!("aaaaa{}ccccc{}eeeee", black_box("bbbbb"), black_box("eeeee"))
two_spaced: format!("{} {}", black_box("bbbbb"), black_box("eeeee"))
worst_case: format!("{} a long piece...", black_box("and even longer argument. not sure why it has to be so long"))
```
```
empty 25 28 3 12.00%
literal 35 29 -6 -17.14%
long 80 46 -34 -42.50%
long_rev 79 45 -34 -43.04%
long_rev_2 111 66 -45 -40.54%
short 73 46 -27 -36.99%
short_rev 74 76 2 2.70%
short_rev_2 107 108 1 0.93%
surround 142 65 -77 -54.23%
two_spaced 111 115 4 3.60%
worst_case 89 101 12 13.48%
```