IDLE: Wrong highlighting when previous line ends with backslash

Bug report

Bug description:

Code like this

str. \
    format

should be coloured the same way as

str.format

Right now IDLE doesn't respect the slash before the newline and thinks that every new line is a new statement.

Similarly in:

x = match if match else \
                   match

The last match should be coloured in like a variable and not a keyword.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-140335
• gh-140337

從 IDLE 的語法醒目提示行為著手，重現涉及換行前反斜線的兩個範例。驗證續行表達式的著色方式與等效的單行表達式相同，包括最後的比對變數；已連結的 PRs gh-140335 和 gh-140337 表明這項工作已經在進行中。