Apply suggested changes to test file

Co-authored-by: Ron Buckton <ron.buckton@microsoft.com>

Author: graphemecluster

tests/cases/compiler/regularExpressionWithNonBMPFlags.ts

@@ -1,3 +1,9 @@
 // @target: esnext
 
+// The characters in the following regular expression are ASCII-lookalike characters found in Unicode, including:
+// - 𝘴 (U+1D634 Mathematical Sans-Serif Italic Small S)
+// - 𝘪 (U+1D62A Mathematical Sans-Serif Italic Small I)
+// - 𝘮 (U+1D62E Mathematical Sans-Serif Italic Small M)
+//
+// See https://en.wikipedia.org/wiki/Mathematical_Alphanumeric_Symbols
 const 𝘳𝘦𝘨𝘦𝘹 = /(?𝘴𝘪-𝘮:^𝘧𝘰𝘰.)/𝘨𝘮𝘶;