[psteinroe]

Stacked on #1063.

The WASM bindings converted LSP positions with their own functions, which #969 fixed for CRLF files. Now they use the shared pgls_line_index::LineIndex, like the native language server, and the index takes over the rules #969 introduced. This changes behaviour in the native language server for positions next to a \r\n:

select 1;\r\n
select 2;
-- (0, 100), a column past the end of line 0:
--   before: offset 10, between the \r and the \n; now: offset 9, before the \r
-- offset 10, between the \r and the \n:
--   before: (0, 10), a column after the \r; now: (0, 9), the end of the line

The LSP says a position can't point between \r and \n, and that a column past the end of a line means the end of the line, which doesn't include its line break.

What the index does now:

• The end of a line is the start of its line break, so before the \r of a \r\n. It records the offsets of the \ns that follow a \r, so LF files pay nothing extra.
• line_col turns an offset between \r and \n into the end of its line, and an offset past the end of the text into the end of the text.
• offset_clamped turns a column inside a character into the start of that character. Before, the native language server returned an offset inside the character, and the WASM bindings moved to the start of the next character. The start matches what fix(lsp): debug assertions at range boundaries, keep client positions on char boundaries #952 does for the native language server, so select '😀'; at UTF-16 column 9 (inside the surrogate pair) is offset 8 in both now. That's the only change for the WASM bindings.
• A lone \r still doesn't end a line, in both.

The WASM bindings keep a LineIndex per document, built on didOpen and didChange, like the native Document, instead of scanning the text on every conversion. changed_range still widens a fix-all edit that changes only one half of a \r\n, since that's about the edit, not the conversion.

Tests: line_breaks_and_wide_characters in pgls_line_index now pins the new behaviour for \r\n (end of line, offset between \r and \n), a lone \r, an offset past the end, and columns inside 2-byte and 4-byte characters in UTF-8 and UTF-16. crlf_belongs_to_the_line_break checks the same through the native from_lsp/to_lsp and fails without this change. The WASM conversion tests from #969 run against the shared index unchanged, apart from the surrogate pair case above, plus a new lone \r test. cargo test -p pgls_line_index -p pgls_lsp -p pgls_wasm, cargo clippy --workspace --all-targets -- -D warnings, and the WASM package's bun run build && bun test (49 pass).

Not covered: the native to_lsp::text_edits doesn't widen edits that change only one half of a \r\n the way the WASM fix-all does, so such an edit (e.g. \r\n to \n) becomes an empty range. Before, it ended at a column after the \r, which editors clamp to the same empty range.

Update: merged main, which brought #952's debug assertions. to_lsp::position now asserts that a position maps back to the offset of its line and column, so an offset between the \r and the \n (mapped to the end of the line) passes. LineIndex::line_col keeps #952's assertion that the offset is inside the text, so the clamp of an offset past the end only applies in release builds, and the line_col(100) case is out of the pgls_line_index test.