You could add custom code that changes the FilterExpression of the RadGrid when the EqualTo filter is applied. Note, however that this would actually make the filter work incorrectly. The text entered in the input would not be equal to the actual data in the data source. More information on the different formats that are used for FilterExpression is available in this article
This said, it is recommended to remove the leading spaces from the names that are stored in the data source. This way the filter functions would work as expected.
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