fix(fmt): use non-zero exit code when formatting fails

[WWRS]

Fixes #28483

• Added a counter in RealFormatter for files that failed to format (usually due to syntax error). If this isn't 0, finish now returns an error.
• Moved related itests to specs

[CLAassistant]

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[marvinhagemeister]

Nit: I feel like the duplicate file part is confusing to read. Maybe it should look something like this?

error: Failed to format 1 file

[WWRS]

This mirrors fmt --check, which reports a result like error: Found 5 not formatted files in 10 files

This PR would cause fmt to produce error: Failed to format 5 files in 10 files

I think all of these are reasonable:

• The suggested error: Failed to format 5 files
• The existing error: Failed to format 5 files in 10 files
• Some clearer message, e.g. error: Failed to format 5 files of 10 checked files

Do you have a preference? And (if option 1 or option 3) should the message in fmt --check be changed to match?

[nayeemrmn]

@WWRS Can you change it to error: Failed to format 5 of 10 checked files? Would be fine either way with changing deno fmt --check to match.

Or let us know if you want us to finish the PR. We want to land this soon

[marvinhagemeister]

Nice work, also +1 on adding tests. Let's get rid of the duplicate file part in the output and then I think it's ready to be merged.

[nayeemrmn]

LGTM. Thanks!