[UNDERTOW-2552] fix: add non-ascii support for big formData value

[halcsi19790320]

FileItem.getValue not works well with non-ascii characters

[shizhenhua01]

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[baranowb]

@halcsi19790320 - could you please update commit message to following format: "[UNDERTOW-12345] description" ?

[baranowb]

@halcsi19790320
Looks like there are checkstyle violations:
Error: /home/runner/work/undertow/undertow/core/src/main/java/io/undertow/util/FileUtils.java:78:9: Line contains a tab character. [FileTabCharacter]
Error: /home/runner/work/undertow/undertow/core/src/main/java/io/undertow/util/FileUtils.java:82:13: Line contains a tab character. [FileTabCharacter]
Error: /home/runner/work/undertow/undertow/core/src/test/java/io/undertow/server/handlers/form/MultipartFormDataParserTestCase.java:267: Line has trailing spaces. [RegexpSingleline]
Error: /home/runner/work/undertow/undertow/core/src/test/java/io/undertow/server/handlers/form/MultipartFormDataParserTestCase.java:343: Line has trailing spaces. [RegexpSingleline]
Error: /home/runner/work/undertow/undertow/core/src/test/java/io/undertow/server/handlers/form/MultipartFormDataParserTestCase.java:356: Line has trailing spaces. [RegexpSingleline]
Error: /home/runner/work/undertow/undertow/core/src/test/java/io/undertow/server/handlers/form/MultipartFormDataParserTestCase.java:371: Line has trailing spaces. [RegexpSingleline]
Error: /home/runner/work/undertow/undertow/core/src/test/java/io/undertow/server/handlers/form/MultipartFormDataParserTestCase.java:373:5: Line contains a tab character. [FileTabCharacter]
Error: /home/runner/work/undertow/undertow/core/src/test/java/io/undertow/server/handlers/form/MultipartFormDataParserTestCase.java:374:1: Line contains a tab character. [FileTabCharacter]
Error: /home/runner/work/undertow/undertow/core/src/test/java/io/undertow/server/handlers/form/MultipartFormDataParserTestCase.java:375:1: Line contains a tab character. [FileTabCharacter]
Error: /home/runner/work/undertow/undertow/core/src/test/java/io/undertow/server/handlers/form/MultipartFormDataParserTestCase.java:376:1: Line contains a tab character. [FileTabCharacter]
Error: /home/runner/work/undertow/undertow/core/src/test/java/io/undertow/server/handlers/form/MultipartFormDataParserTestCase.java:377:1: Line contains a tab character. [FileTabCharacter]
Error: /home/runner/work/undertow/undertow/core/src/test/java/io/undertow/server/handlers/form/MultipartFormDataParserTestCase.java:378:1: Line contains a tab character. [FileTabCharacter]
Error: /home/runner/work/undertow/undertow/core/src/test/java/io/undertow/server/handlers/form/MultipartFormDataParserTestCase.java:379: Line has trailing spaces. [RegexpSingleline]

[ropalka]

Creating Strings during stream parsing was wrong.

[halcsi19790320]

I updated this commit. I hope it is good now.