feat: sync workbench fixes and upstream cherry-picks

[saltines321-debug]

Summary

• Cherry-picked 25+ upstream PRs with bug fixes and improvements
• Applied null-safety hardening (PR fix: guard toolbar ViewPager touch events #1 original fixes)
• Fixed resource leaks, crashes, and UI issues
• Cleaned up build system (removed ancient updated-flavor breakage)
• CI workflow: dropped apt-android-5, restored Gradle wrapper

PRs included

• Added display of extra key "SPACE" as "␣" (U+2423). termux/termux-app#4250: Display SPACE key as unicode symbol
• Add blinking support for 'cursor style' CSI termux/termux-app#2600: Cursor blinking CSI support
• Clear LineWrap flag when clearing lines using blockSet. termux/termux-app#2971: Clear LineWrap on blockSet
• fix(terminal-emulator): flush output stream after writing to PTY termux/termux-app#5104: Flush PTY output stream
• Close FileInputStream in code termux/termux-app#5072: Close FileInputStream (try-with-resources)
• Put space between URLs and trailing Punctuation termux/termux-app#2932: Fix URL trailing space
• Changed: Correct typo and use keyboard keys formatting instead of code snippet one in README.md termux/termux-app#4994: Fix keyboard key formatting
• fix the problem Cursor colour turns grayish black on turning on dark …#3738 termux/termux-app#3779: Fix cursor color in dark mode
• Fix/Allow fullscreen mode to consume status bar area on some devices termux/termux-app#1923: Fullscreen mode with display cutout
• Fix Samsung floating window layout flicker termux/termux-app#5090: Fix Samsung floating window flicker
• Fix: terminal freezes when activity is destroyed while new instance already bound termux/termux-app#5094: Fix terminal freeze on activity recreate
• Fix fullscreen mode on Android 11+ where navigation bar was not hidden termux/termux-app#5007: Fullscreen mode Android 11+
• Fix(terminal-emulator): Trim synthetic wide-char trailing blank on copy (#1397) termux/termux-app#5046: Trim synthetic wide-char trailing blank
• And more...