Rollup merge of rust-lang#147165 - Muscraft:subtract-code-offset, r=davidtwco

test: Subtract code_offset from width for ui_testing

`annotate-snippets` does not have a "UI test" mode like `rustc`, [where the code offset is not subtracted from the column width](https://github.com/rust-lang/rust/blob/f34ba774c78ea32b7c40598b8ad23e75cdac42a6/compiler/rustc_errors/src/emitter.rs#L1985-L1987). This makes it so `annotate-snippets` will shift the output for some very long tests 5 - 7 columns to the left. As part of my work to have `rustc` use `annotate-snippets`, and to reduce the test differences between the two, I figured it would be best if `rustc` started subtracting the code offset from the width as well.

The first commit exists to keep the test output changes of adding a new line to a test separate from adding the `--diagnostic-width` flag in the second commit. This makes it easier to verify that adding the flag does not affect the test's output.

[Zulip discussion](https://rust-lang.zulipchat.com/#narrow/channel/147480-t-compiler.2Fdiagnostics/topic/annotate-snippets.20hurdles)

Author: matthiaskrgr

tests/ui/option_env_unwrap.stderr

@@ -19,7 +19,7 @@ LL |     let _ = option_env!("PATH").expect("environment variable PATH isn't set
 error: this will panic at run-time if the environment variable doesn't exist at compile-time
   --> tests/ui/option_env_unwrap.rs:14:13
    |
-LL |     let _ = option_env!("__Y__do_not_use").unwrap(); // This test only works if you don't have a __Y__do_not_use env variable in your env...
+LL |     let _ = option_env!("__Y__do_not_use").unwrap(); // This test only works if you don't have a __Y__do_not_use env variable in you...
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: consider using the `env!` macro instead

tests/ui/too_long_first_doc_paragraph.stderr

@@ -42,7 +42,7 @@ LL | | /// gravida non lacinia at, rhoncus eu lacus.
 error: first doc comment paragraph is too long
   --> tests/ui/too_long_first_doc_paragraph.rs:65:1
    |
-LL | / /// Some function. This doc-string paragraph is too long. Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lore...
+LL | / /// Some function. This doc-string paragraph is too long. Lorem Ipsum is simply dummy text of the printing and typesetting industr...
 LL | |
 LL | | ///
 LL | | /// Here's a second paragraph. It would be preferable to put the details here.