Auto merge of #15751 - avinash-vijayaraghavan:testing-csserror, r=cbrewster

first stab. added ServoUrl as a parameter to report_error(...) of Par…

@jdm @SimonSapin
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1. Added ServoUrl as a parameter to report_error(...) of ParseErrorReporter trait.
2. I am not sure how to handle the case of impl ParseErrorReporter for CSSErrorReporter and MemoryHoleReporter, so have not made any changes  (other than adding ServoUrl arg) to report_error implementations for these.
3. In StdoutErrorReporter i have added the ServoUrl arg to the info! function,
4. I would like to know if i am on the correct path and clarify what else needs to be done.

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- [ X] `./mach build -d` does not report any errors
- [ ] `./mach test-tidy` does not report any errors
- [ ] These changes fix #15708 (github issue number if applicable).

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- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because wanted to clarify before writing tests

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