Auto merge of #20320 - kwonoj:feat-wr-revision, r=jdm

feat(capture_webrender): write webrender revision into text

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Relates to https://github.com/servo/servo/pull/20315#issuecomment-373819735.

This PR try to generate `wr.txt` when trigger webrender capture. By reading gecko's implementation at [here](https://github.com/mozilla/gecko-dev/blob/3b8e63c66ae1989cfc2c7fb48ca9e025a3828e74/gfx/doc/README.webrender#L53), it seems gecko's build script generates txt file for containing revision of webrender and read it each time trigger capturing.

In this PR tries to similar in cruxwise with small differences:
- `cargo build` reads `cargo.lock`, export it into `${OUT_DIR}/`, included via macro in build time.
- when capturing triggered, those revision will be written as `wr.txt`.

Probably point of discussion & need to be updated in PR if necessary:
~- Is it acceptable `mach` generates module file on build bootstrapping? Should there be other recommendation?~ Now cargo build takes care of generation.

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- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #20295 (github issue number if applicable).

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