fix(devServer): support html asset emit when using writeToDisk

[ycjcl868]

Checklist

• npm test passes
• tests are included
• documentation is changed or added
• commit message follows commit guidelines

Description of change

• any feature?
• close https://github.com/umijs/umi/ISSUE_URL

[codecov]

Codecov Report

Merging #6108 (c3a00b1) into master (10b4e02) will increase coverage by 0.14%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master    #6108      +/-   ##
==========================================
+ Coverage   82.94%   83.09%   +0.14%     
==========================================
  Files         158      158              
  Lines        3501     3502       +1     
  Branches      941      942       +1     
==========================================
+ Hits         2904     2910       +6     
+ Misses        588      582       -6     
- Partials        9       10       +1     

Impacted Files	Coverage Δ
...c/plugins/commands/build/applyHtmlWebpackPlugin.ts	73.33% <66.66%> (+0.91%)	⬆️
...set-built-in/src/plugins/commands/generateFiles.ts	47.82% <0.00%> (+8.69%)	⬆️
...preset-built-in/src/plugins/features/devScripts.ts	54.16% <0.00%> (+12.50%)	⬆️

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