Auto merge of #79762 - Swatinem:remap-doctest-coverage, r=Swatinem

Auto merge of #79762 - Swatinem:remap-doctest-coverage, r=Swatinem

Remap instrument-coverage line numbers in doctests

This uses the `SourceMap::doctest_offset_line` method to re-map line
numbers from doctests. Remapping columns is not yet done, and rustdoc
still does not output the correct filename when running doctests in a
workspace.

Part of #79417 although I dont consider that fixed until both filenames
and columns are mapped correctly.

r? `@richkadel`

I might jump on zulip the comming days. Still need to figure out how to properly write tests for this, and deal with other doctest issues in the meantime.