fix(fs): report read errors of readTextFileLines (#3625)

* fix(fs): report read errors of readTextFileLines

In plugins/fs/src/commands.rs read_text_file_lines_next, a read error was
mapped to "not done, empty line", so a persistent error such as EISDIR
(File::open of a directory succeeds on Unix) made the iterator yield ""
forever and the error was swallowed.

The command now closes the resource and returns the error; the JS iterator
resets its rid so a new iteration starts over. api-iife.js regenerated. E2E
spec iterates a directory and expects a rejection.

* fix(fs): close the file when a readTextFileLines loop exits early

In plugins/fs/guest-js/index.ts readTextFileLines, the async iterator did
not implement return(), so breaking out of a for await loop left the
StdLinesResource (an open file) in the webview resource table.

return() now closes the resource and resets the iterator. api-iife.js
regenerated. E2E spec breaks out of a loop, checks the resource id is no
longer valid and that iterating again starts over.

.changes/fix-fs-read-lines-error.md

@@ -0,0 +1,6 @@
+---
+fs: patch
+fs-js: patch
+---
+
+Fixed `readTextFileLines` yielding empty lines forever when reading fails (e.g. on a directory). The read error is now reported: the iterator rejects and the file is closed.

.changes/fix-fs-read-lines-return.md

@@ -0,0 +1,6 @@
+---
+fs: patch
+fs-js: patch
+---
+
+Fixed `readTextFileLines` leaving the file open until the webview is destroyed when a `for await` loop over it exits early (`break`, `return` or `throw`). The iterator now implements `return()`, which closes the file.