Add case-sensitive glob support to syntax mapping

to allow us to map `BUILD` case sensitively to Python for Skylark

src/syntax_mapping/builtins/README.md

@@ -20,9 +20,9 @@ syntax mappings defined by all TOML files, and embed them into the binary.
 
 ## File syntax
 
-Each TOML file should contain a single section named `mappings`, with each of
-its keys being a language identifier (first column of `bat -L`; also referred to
-as "target").
+Each TOML file should contain a single section named `mappings` and/or a single
+section named `case_sensitive_mappings`, with each of its keys being a language
+identifier (first column of `bat -L`; also referred to as "target").
 
 The value of each key should be an array of strings, with each item being a glob
 matcher. We will call each of these items a "rule".

src/syntax_mapping/builtins/common/50-bazel.toml

@@ -1,2 +1,2 @@
-[mappings]
+[case_sensitive_mappings]
 "Python" = ["BUILD"]