You can do this in two steps:
First, convert the evolution email folder to an mbox file.
You can use this script: https://github.com/bluebird75/maildir2mbox or http://stackoverflow.com/questions/2501182/convert-maildir-to-mbox/8930126#8930126 to convert the folder to a mbox file.
Tips: the directory should have structure like
You can create directories like that and copy all email files to the
Second, import the mbox file to Thunderbird.
Thunderbird by default does not provide this function now. You need to install the ImportExportTools plugin to add this function: https://addons.mozilla.org/en-US/thunderbird/addon/importexporttools/
After the emails are imported to Thunderbird folders, you can copy them to the imap directories.