Add a formatting step using `mdformat` as part of `generate_mkdocs.py` #26024

Job	Run time
cargo fmt	19s
pre-commit	42s
Determine changes	7s
mkdocs	2m 17s
python package	1m 20s
cargo clippy	1m 57s
cargo test (linux)	4m 0s
cargo udeps	1m 56s
cargo fuzz	5m 19s
cargo test (wasm)	1m 15s
cargo test (windows)	6m 58s
test scripts	51s
benchmarks	4m 42s
formatter instabilities and black similarity	3m 41s
test ruff-lsp	25s
ecosystem	13m 27s
	49m 16s

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