ICU-22813 Rise the size of the buffers used for the command strings at pkgdata

[clopez]

The tool pkgdata uses snprintf() to build the strings of the commands that will execute later during the install process. But the maximum size of this buffers is not enough when there is a long path.

This has caused issues on some CI systems that use very long paths, causing the install process to produce a wrong result.

The maximum path on Linux is 4096 (defined as PATH_MAX at <linux/limits.h>) So the size of SMALL_BUFFER_MAX_SIZE should be 4096 to avoid errors related to truncated paths.

Checklist

• Required: Issue filed: https://unicode-org.atlassian.net/browse/ICU-22813
• Required: The PR title must be prefixed with a JIRA Issue number.
• Required: The PR description must include the link to the Jira Issue, for example by completing the URL in the first checklist item
• Required: Each commit message must be prefixed with a JIRA Issue number.
• Issue accepted (done by Technical Committee after discussion)
• Tests included, if applicable
• API docs and/or User Guide docs changed or added, if applicable

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[markusicu]

lgtm tnx!
Longer-term, we should rewrite this kind of code to print into a std::string, which we can use here since it's not part of the ICU runtime libraries.