Issue #295: three clicks select the line, four clicks the page (#366)

* Text: find the word and the line around a glyph

PageText gets word_at(i) and line_at(i). Each returns the first and
last glyph of the word or the line around glyph i, or None when i is
past the end of the page's text. A word stops at a word gap, a blank
glyph or a line end. A line is the run of glyphs with the same line
number.

The canvas's double-click used its own loop for this, which indexed the
glyph, line and gap arrays directly. It now calls word_at, which reads
them with get(). Double-clicking selects the same words as before.

Test: render words_and_lines_around_a_glyph, on two lines with a blank
glyph, a word gap and a line break.

* Issue #295: three clicks select the line, four clicks the page

With the Select tool, quick clicks on text widen the selection like
Acrobat: two clicks select a word (as before), three the line, four or
more all the text on the page. A third click used to clear the
selection.

egui counts only up to triple clicks and reports a fourth quick click
as another triple, so the view keeps its own count of the current run.
A single click resets it and a pause ends it.

With the markup tools (Highlight and the like) and Redact, a
double-click already turns the word into a mark at once. They stop at
the word, so more clicks don't stack line or page marks.

Tests: ui-egui quick_clicks_select_a_word_then_the_line_then_the_page
and quick_clicks_with_the_highlighter_mark_only_the_word.

parity: view.text-select cites the tests. The notes say what is
missing: paragraph selection, and Ctrl/⌘+A across the whole document
(it selects the current page).

* Clippy: as_chunks in the signature preview test (follow-up to #355)

Clippy 1.99 rejects chunks_exact with a constant chunk size
(chunks_exact_to_as_chunks), so `cargo clippy --workspace --all-targets
-- -D warnings` fails on main since #355. Use as_chunks, as #360 did
for the test above it.

---------

Co-authored-by: Brandon Thomas <echelon@gmail.com>

parity/acrobat-features.toml

@@ -1466,8 +1466,8 @@ milestone = "M3"
 status = "shipped"
 commands = []
 tools = []
-evidence = ["crates/ui-egui/tests/ui.rs::drag_selects_text_and_copy_returns_it", "crates/ui-egui/tests/ui.rs::selection_works_in_every_view_rotation"]
-notes = ""
+evidence = ["crates/ui-egui/tests/ui.rs::drag_selects_text_and_copy_returns_it", "crates/ui-egui/tests/ui.rs::selection_works_in_every_view_rotation", "crates/ui-egui/tests/text_select.rs::quick_clicks_select_a_word_then_the_line_then_the_page", "crates/ui-egui/tests/text_select.rs::quick_clicks_with_the_highlighter_mark_only_the_word"]
+notes = "Drag to select; with the Select tool, quick clicks select a word (two), the line (three) or all the text on the page (four). The markup and Redact tools mark a double-clicked word and stop there. Missing: paragraph selection, and ⌘A across the whole document (it selects the current page)."
 
 [[feature]]
 id = "view.copy-text"