Fix bottom rows being clipped when the panel is resized at high DPI

[leoshone]

Fix bottom rows being clipped when the panel is resized at high DPI

The bug

On a monitor whose DPI scale is not 100%, expanding a JSON tree fully and
scrolling to the bottom leaves the last few rows physically unreachable: the
vertical scrollbar reports that it is at the end, but the bottom rows are
simply outside the visible panel. The node path box at the bottom of the panel
disappears completely. The larger the panel (and the higher the DPI scale),
the more rows are lost.

Measured on a 150% DPI display (JSON Viewer docked, panel client 394x968):

what	before the fix
tree control bottom, in panel client coordinates	1181 px (213 px below the panel)
unreachable rows at 100% zoom (item height 22 px)	~10 rows
node path edit box	115 px below the panel, fully invisible

Root cause

JsonViewDlg::AdjustDocPanelSize() multiplied the size delta between the
current panel size and the initially recorded one by CUtility::GetDesktopScale():

auto newDeltaHeight = nHeight - m_lfInitialClientHeight;
auto addHeight      = static_cast<int>((newDeltaHeight - m_lfDeltaHeight) * fDeskScale);

nHeight comes from WM_SIZE and m_lfInitialClientHeight from
GetClientRect - both are already in physical pixels. Multiplying the
delta by the DPI scale again makes the child controls grow s times faster
than the panel itself on any scaled display (s > 1). The tree control
computes its scroll range from its own (oversized) client height, so its
scrollbar is convinced it has reached the end while the overflow rows are
clipped by the parent dialog. At 100% scaling (s == 1) the error is exactly
zero, which is why the bug only shows up on scaled monitors.

The fix

Position the resizable controls from the current client size instead of
accumulating scaled deltas:

• the template layout of the four controls (search box, search button, tree,
  node path box) is captured once when the dialog is created;
• on every WM_SIZE each control is placed at template rect + unscaled
  delta, so its designed margins to the panel edge are preserved at any DPI;
• the tree height is derived as "everything between the tool bar row and the
  node path box", with the node path box pinned to the bottom of the client
  area - the layout is now self-correcting instead of accumulated.

This also fixes two adjacent effects of the same arithmetic: the needless
horizontal scrollbar caused by the oversized tree width, and the drift
between repeated resizes caused by truncating scaled deltas.

Verification

Measured with live Win32 geometry probes against the real plugin inside
Notepad++, at 150% DPI, with the tree fully expanded (TVM_GETVISIBLECOUNT,
TVM_GETNEXTITEM(TVGN_LASTVISIBLE), control rects mapped into the panel's
client space):

• before: tree bottom 213 px below the panel client area, last visible row
  reported as the final one while it was clipped;
• after: tree bottom 36 px above the panel bottom (the space of the node path
  box), all 91 rows of the test document reachable after scrolling to the
  bottom, node path box visible again;
• re-measured across five window resizes (+150 px, +300 px, -200 px, back):
  no drift, overflow stays at zero;
• existing E2E suites (zoom persistence, per-tab snapshot, expansion on
  refresh, draw-on-open, jsonc recognition) all pass unchanged.

[SinghRajenM]

Please share the before after comparison.

[leoshone]

Here is the before/after comparison, taken in the same portable Notepad++ - same document (91 nodes, fully expanded), same window size, zoom 100%. Only the plugin DLL differs between the two runs.

Before - the tree is scrolled to the very bottom (scrollbar reports the end), yet the bottom rows are physically outside the panel and the node path box is gone:

After - all rows reachable, the horizontal scrollbar is back inside the tree client area, and the node path box reappears:

Measured geometry at 150% DPI:

what	before	after
tree bottom vs panel client area	213 px below the panel	36 px inside (the node path box area)
unreachable rows at 100% zoom (item height 22 px)	~10	0
node path edit box	115 px below the panel, fully invisible	visible, pinned to the panel bottom
vertical scrollbar	lower part clipped	fully visible
across 5 window resizes (+150 px, +300 px, -200 px, back)	-	no drift, overflow stays at 0

The screenshots were produced with a live geometry probe (control rects mapped into the panel's client space, TVM_GETNEXTITEM(TVGN_LASTVISIBLE) for the reachable row), so the numbers above are measured, not estimated.