Support --learn for inline expectations via learnEdits

`codeql test run --learn` could previously only rewrite `.expected`
files; inline expectations (the `// $ Alert` comments checked by
`InlineExpectationsTest`) had to be fixed by hand. This teaches the
shared test library to compute those source edits so the test runner
can apply them.

The `test-postprocess` query now exposes a `learnEdits` relation
(`file, line, operation, startColumn, endColumn, text`) describing the
minimal source rewrite that would make the inline expectations match the
actual query results. It covers:

  - appending a fresh comment carrying every tag learned for a line that
    has an unexpected result and no existing comment to merge into;
  - rewriting an existing expectation comment as a whole so it matches
    the current results: dropping fixed-spurious tags, promoting a
    `MISSING:` expectation that now fires, clearing a stale `SPURIOUS:`
    annotation, and merging in freshly learned tags, re-rendering the
    remaining expectations (or deleting the comment when none remain);
  - preserving expectations this test does not own -- e.g. a tag
    annotated with a different query's id that shares the source file --
    and any trailing regular note (`// $ Alert // note`);
  - recording any unexpected result, not just `Alert`.

The comment syntax comes from the `getStartCommentMarker` /
`getEndCommentMarker` markers added to `InputSig` in the previous commit,
so `LearnEditsImpl` renders each edit in the target file's own syntax and
stays language-agnostic. Edits are emitted as a query predicate rather
than applied here: the engine consumes `learnEdits` only under `--learn`
and ignores it otherwise, so ordinary `test run` output is unchanged. The
supporting predicates are wrapped in a `private module LearnEditsImpl` so
only the `query predicate learnEdits` is re-exposed.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 1adfa307-c48e-43f5-94e3-8286e4a8c083

Author: d10c