Fix styled-text note hyperlink click detection

[eduralph]

Summary

User impact: When you view a Note that contains a web link, clicking in the empty space beside the link or below the last line of text unexpectedly opens the link in your browser — even though you never clicked on the link itself. Any click near a link that ends a line or the note can launch the browser by mistake.

This makes Gramps confirm the pointer is really over the link's text before treating a click as a link.

Reported in Mantis #8841.

What to look at

The Note viewer decides whether a click hit a link by asking GTK for the "nearest" text position, which snaps empty-area clicks onto the end of the text and its trailing link. The fix adds a check that the pointer is genuinely inside a character's rendered rectangle before counting it as a link hit. To reproduce: on maintenance/gramps61, create a Note, paste a URL on its own line, save, and reopen in read-only view. Click in the empty area below or to the right of the URL — before the fix the browser opens; after the fix the empty-area click does nothing, while clicking on the URL still opens it.

Root cause

Gtk.TextView.get_iter_at_location(x, y) is a GTK3 API that returns the "nearest" text iterator for any point, including a click in the empty area beside/below text — it never returns "no iter". In styledtexteditor.py, on_motion_notify_event() (lines 424–456) sets iter_at_location from the click at line 435, then uses that position directly to look up URLs (via match_check()) and internal link tags. An empty-area click snaps to the end of the text and matches the link if one ends there; on_button_press_event() (lines 501–516) then opens the link when self.url_match is set, and do_match_changed() (line 404) keeps self.url_match in sync.

Fix

The fix (in gramps/gui/widgets/styledtexteditor.py) adds a new private method _pointer_over_iter(x, y, text_iter) that uses get_iter_location() to confirm the point (x, y) is genuinely inside a character's bounding rectangle. Because get_iter_at_location() advances past a glyph when the click lands in that glyph's trailing (right) half (it adds Pango's trailing count), the character under the pointer may be the one before text_iter; the helper therefore checks the rectangle of the char at the iter and, on a miss, the char immediately before it. Both the URL regexp match path (match_check()) and the internal link-tag loop are guarded by this check:

if self._pointer_over_iter(x, y, iter_at_location):
    self.match = self.textbuffer.match_check(...)
    ... link-tag loop ...
else:
    self.match = None

This ensures that a click to the right of the URL on its line is excluded (past the last glyph's rectangle); a click below the last line is excluded (below every line's rectangle); and a click anywhere on the URL glyph, left or right half, still matches (point inside the char's or its predecessor's rectangle → link still opens). Both URL matches and internal link tags are guarded, so neither hyperlink flavour can open on an empty-area click, and neither is lost on a real on-glyph click.

Verification

• Claim: get_iter_at_location() snaps even out-of-bounds clicks; the fix gates both URL matches and internal link tags on a real glyph hit (checking the snapped char and its predecessor), clears the match otherwise, and leaves the match→open path intact.
• Checked: on maintenance/gramps61 — gramps/gui/widgets/styledtexteditor.py:435 sets iter_at_location from the user click (nearest-iter semantics per GTK3 docs / match_check behaviour). Patched: the URL match_check() and the link-tag loop now sit inside an if self._pointer_over_iter() block, with an else clause setting self.match = None for out-of-bounds clicks; _pointer_over_iter() uses get_iter_location() to confirm the point is inside the char at the iter or, on a miss, the char before it (covering the trailing-half advance so a real click on a link glyph's right half still opens). The signal path is unbroken: styledtexteditor.py:450–451 still emits "match-changed" when self.match changes, do_match_changed() still updates self.url_match (line 404, preimage), and on_button_press_event() (lines 511–516, preimage) consumes self.url_match and calls _open_url_cb() only when set.
• Test: No core unit test ships — the behaviour is a GUI hit-test, not headless-testable. Coverage is a committed AT-SPI/dogtail repro in the gramps-testbed harness (not part of this PR), engine/interface/test_bug_0008841_note_link_hittest.py, red without the fix and green with it: before an empty-area click snaps to the URL end, match_check() includes that offset, self.match is set, and the non-editable view calls _open_url_cb() so the "does not open" assertion fails; after, _pointer_over_iter() returns False, self.match stays None, no browser launch occurs, and on-glyph clicks still match so the positive assertion passes both legs.

Fixes #8841