fix: keep placeholder within text margins (DLineEditEx)

[mhduiy]

修复：锁屏/登录密码框占位符省略后与功能图标重叠

问题

锁屏/登录界面在「焦点态 + 空文本 + 居中 placeholder」分支手动重绘 placeholder 时，省略与绘制使用的是 DLineEditEx 整框 rect() 宽度，未扣除内嵌 QLineEdit 的 textMargins()（即大写、显示密码、认证状态、密码提示等图标的避让区），导致长错误/提示文案省略后仍横跨整框、与左右功能图标重叠。

改动

• 仓库：dde-session-shell
• 文件：src/widgets/dlineeditex.cpp — DLineEditEx::paintEvent()
• 将 placeholder 的省略（elidedText 宽度参数）与绘制（drawText 目标矩形）从整框 rect() 约束到「扣除内嵌 QLineEdit 的 textMargins() 后的文本可用矩形」内
• 通过 le->mapTo(this, QPoint(0,0)) 将内嵌 QLineEdit（子控件）坐标映射到 DLineEditEx（QFrame，QPainter(this) 绘制坐标系），避免父子控件坐标换算导致省略宽度偏差
• tooltip 逻辑保持不变；不涉及后端 DBus / deepin-authenticate / DTK 控件 / DConfig / 翻译 / QSS

验证

• 语法/类型检查：g++ -std=c++17 -fsyntax-only（Qt6 / dtk6widget 头文件路径）通过，仅余一处与本次改动无关的既有 QGuiApplication::fontChanged 弃用告警
• 代码审核：已通过（坐标映射正确性、textMargins 读取时机、未设 textMargins 场景回归、Qt6 路径）
• 编译构建：基于 master 重建并构建通过，主包 dde-session-shell_5.6.12.1_amd64.deb 已产出
• 运行时 GUI 自测：英文 locale 或调大字号/缩放下、设较长密码提示、锁屏/登录输错密码后清空密码框，确认 placeholder 省略后止于左右图标内侧、不再重叠；中文短文案回归正常（待人工确认）

关联

• Multica issue: DDE-67
• PMS: https://pms.uniontech.com/bug-view-351887.html (BUG-351887)

说明

本次 PR 仅含业务修复 src/widgets/dlineeditex.cpp；打包适配改动（debian/*）为本地构建所需，未纳入本 PR。PR 保持 draft/待审核状态，请勿合并。

Summary by Sourcery

Bug Fixes:

• Ensure centered placeholders in lock/login password fields are elided and drawn within the usable text rectangle, avoiding overlap with left/right functional icons.

[deepin-ci-robot]

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[deepin-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: mhduiy

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[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Adjusts DLineEditEx placeholder rendering so that elided placeholder text is constrained to the inner QLineEdit’s text area, preventing overlap with left/right icons, while keeping existing tooltip behavior intact.

Sequence diagram for updated placeholder painting in DLineEditEx::paintEvent

sequenceDiagram
    participant DLineEditEx
    participant QLineEdit as lineEdit
    participant QPainter as pa
    participant QFontMetrics as fm

    DLineEditEx->>QPainter: QPainter(this)
    DLineEditEx->>QFontMetrics: QFontMetrics(pa.font())
    DLineEditEx->>QLineEdit: lineEdit()
    DLineEditEx->>QLineEdit: placeholderText()
    QLineEdit-->>DLineEditEx: placeholderText
    DLineEditEx->>QLineEdit: textMargins()
    QLineEdit-->>DLineEditEx: tm
    DLineEditEx->>QLineEdit: mapTo(this, QPoint(0,0))
    QLineEdit-->>DLineEditEx: topLeftInParent
    DLineEditEx->>DLineEditEx: build lineEditRect(topLeftInParent, le->size())
    DLineEditEx->>DLineEditEx: build textRect(lineEditRect.adjusted(tm.left(), tm.top(), -tm.right(), -tm.bottom()))
    DLineEditEx->>QFontMetrics: elidedText(placeholderText, Qt::ElideRight, textRect.width())
    QFontMetrics-->>DLineEditEx: elidedText
    DLineEditEx->>QPainter: drawText(textRect, Qt::AlignCenter | Qt::TextSingleLine, elidedText)

Loading

File-Level Changes

Change	Details	Files
Constrain placeholder elision and drawing to the QLineEdit text area accounting for textMargins and parent-child coordinate offsets.	Replace use of the full DLineEditEx rect for placeholder elidedText width and drawText target with a calculated textRect derived from the embedded QLineEdit Use QLineEdit::textMargins to compute the actual usable text area, subtracting icon padding from the placeholder rendering region Map the embedded QLineEdit’s origin into the DLineEditEx coordinate system via mapTo(this, QPoint(0, 0)) to build an accurate lineEditRect Update elidedText width parameter to textRect.width() and draw the centered single-line placeholder within textRect while leaving tooltip logic unchanged	src/widgets/dlineeditex.cpp

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