Shift from ARGS to EXTRA-ARGS where possible (#5602)

Adds minimal defaults for codegen so that those tests don't need to
specify the full command line.

Moves driver/testdata/compile to check/testdata/basics/raw_sem_ir, which
seems like it better reflects the focus. Removes the textual IR test
because we have plenty of those now.

Moves a multiline token diagnostic test to parse because (a) diagnostics
doesn't have other tests and (b) this is really testing the way that
parse structures the location.

Drops `--include-diagnostic-kind` from some driver tests that aren't
testing a diagnostic, so the flag felt a bit like noise (even before
this change, there are a few tests that don't specify it because they're
not intended to test an emitted diagnostic, just high-level diagnostic
behaviors).

Adds some comments to reflect my understanding of why a test exists,
when I was pausing to think about it.

Modifies the stdin test to do more dumps; which happens to expose we
currently misbehave.

toolchain/codegen/testdata/objcode/basic.carbon

@@ -2,7 +2,7 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// ARGS: --include-diagnostic-kind compile --no-prelude-import --target=x86_64-unknown-linux-gnu --output=%t %s
+// EXTRA-ARGS: --no-prelude-import --target=x86_64-unknown-linux-gnu --output=%t
 //
 // TODO: Add a way to write some basic tests for object file outputs.
 // AUTOUPDATE