Rename top-level LICENSE.txt files to LICENSE.TXT

This makes all the license filenames uniform across subprojects.

Differential Revision: https://reviews.llvm.org/D98380

GitOrigin-RevId: baf637dcde8ccc24fd6ffbc82d8321ba18ec857f
diff --git a/LICENSE.txt b/LICENSE.TXT
similarity index 100%
rename from LICENSE.txt
rename to LICENSE.TXT