progress: if not escaped, backslashes `\` not printed on the progress stream dockerfile steps

However, prints when escaped or put within "..":

Minimal repro dockerfile:

FROM mcr.microsoft.com/windows/nanoserver:ltsc2022

RUN echo C:\hello\world\path
RUN echo C:\\hello\\escaped\\path
RUN echo "C:\hello\quoted\path"

Result:

#5 [2/4] RUN echo C:helloworldpath
#5 1.359 C:\hello\world\path
#5 DONE 1.7s

#6 [3/4] RUN echo C:\hello\escaped\path
#6 1.734 C:\\hello\\escaped\\path
#6 DONE 2.1s

#7 [4/4] RUN echo "C:\hello\quoted\path"
#7 1.765 "C:\hello\quoted\path"
#7 DONE 2.1s

With classic docker build:

Result:

Step 2/4 : RUN echo C:\hello\world\path
 ---> Running in 94d37a87e491
C:\hello\world\path
 ---> Removed intermediate container 94d37a87e491
 ---> b098d8792b7c
Step 3/4 : RUN echo C:\\hello\\escaped\\path
 ---> Running in d2fcea089fb1
C:\\hello\\escaped\\path
 ---> Removed intermediate container d2fcea089fb1
 ---> e6c9869a97f8
Step 4/4 : RUN echo "C:\hello\quoted\path"
 ---> Running in 2e2c603aebe2
"C:\hello\quoted\path"
 ---> Removed intermediate container 2e2c603aebe2
 ---> 56ba89eb540e

No source files or tests are named. Start by tracing BuildKit's progress-stream handling for Dockerfile RUN commands and compare it with the classic docker build output using the provided Windows Dockerfile. Done means unescaped backslashes remain visible in progress output, while escaped and quoted cases retain their current behavior.