patch 9.2.0387: DECRQM request may leave stray chars in terminal

patch 9.2.0387: DECRQM request may leave stray chars in terminal

Problem:  Sending DECRQM from handle_version_response() caused DECRPM
          responses to arrive during user input processing, leaving
          bytes in typebuf when clear_showcmd() ran.  This made
          visual-mode showcmd (e.g. "7" line count after V<C-D><C-D>)
          intermittently disappear, failing many screendump tests on CI.
Solution: Move DECRQM request out of handle_version_response() and send
          it at startup via may_req_decrqm(), following the existing
          may_req_termresponse() and may_req_bg_color() pattern.
          Add TPR_DECRQM property set per terminal from the DA2 reply,
          and route DECRQM sends through a may_req_decrqm() helper using
          the termrequest_T pattern, skipping terminals known to
          mishandle it (Foxe Chen, Hirohito Higashi).

fixes:  #19852
closes: #19938

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Co-Authored-By: Hirohito Higashi <h.east.727@gmail.com>
Co-Authored-By: Foxe Chen <chen.foxe@gmail.com>
Signed-off-by: Hirohito Higashi <h.east.727@gmail.com>
Signed-off-by: Foxe Chen <chen.foxe@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>