[ADT] Deprecate StringRef::{starts,ends}with_insensitive

[kazu]

Summary

This patch deprecates StringRef::{starts,ends}with_insensitive as
their uses have migrated to {starts,ends}_with_insensitive,
respectively.

[dblaikie]

SGTM

[tmatheson]

Do we need to deprecate, or can we simply remove the old definitions?

[MaskRay]

In D152108#4449023, @tmatheson wrote:

Do we need to deprecate, or can we simply remove the old definitions?

startswith_insensitive appears to be used rare enough, mostly used within llvm-project. I think we can just remove them.

llvm/include/llvm/ADT/StringRef.h

[[nodiscard]] bool starts_with(StringRef Prefix) const {
              compareMemory(Data, Prefix.Data, Prefix.Length) == 0;
     }
     [[nodiscard]] bool startswith(StringRef Prefix) const {
       return starts_with(Prefix);
     }
 
     /// Check if this string starts with the given \p Prefix, ignoring case.
     [[nodiscard]] bool starts_with_insensitive(StringRef Prefix) const;
-    [[nodiscard]] bool startswith_insensitive(StringRef Prefix) const {
+    [[nodiscard]] LLVM_DEPRECATED(
+        "Use starts_with_insensitive instead",
+        "starts_with_insensitive") bool startswith_insensitive(StringRef Prefix)
+        const {
       return starts_with_insensitive(Prefix);
     }
 
     /// Check if this string ends with the given \p Suffix.
     [[nodiscard]] bool ends_with(StringRef Suffix) const {
       return Length >= Suffix.Length &&
              compareMemory(end() - Suffix.Length, Suffix.Data, Suffix.Length) ==
                  0;
     }
     [[nodiscard]] bool endswith(StringRef Suffix) const {
       return ends_with(Suffix);
     }
 
     /// Check if this string ends with the given \p Suffix, ignoring case.
     [[nodiscard]] bool ends_with_insensitive(StringRef Suffix) const;
-    [[nodiscard]] bool endswith_insensitive(StringRef Suffix) const {
+    [[nodiscard]] LLVM_DEPRECATED(
+        "Use ends_with_insensitive instead",
+        "ends_with_insensitive") bool endswith_insensitive(StringRef Suffix)
+        const {
       return ends_with_insensitive(Suffix);
     }
 
     /// @}
     /// @name String Searching
     /// @{
 
     /// Search for the first character \p C in the string.