chore: migrate base::StringPiece to std::string_view (#40915)

* chore: migrate from base::StringPiece to std::string_view in keyboard_util.cc

* chore: migrate from base::StringPiece to std::string_view in error_thrower.cc

* chore: migrate from base::StringPiece to std::string_view in electron_api_web_contents.cc

* chore: migrate from base::StringPiece to std::string_view in gin_helper/dictionary.h

* chore: migrate from base::StringPiece to std::string_view in electron_api_url_loader.cc

* chore: phase out internal use of base:::StringPiece

`base::StringPiece` is being phased out upstream. Its code has been
removed upstream and it's just a typedef for `std::string_view`.

They haven't removed the typedef yet, so this PR tries to get ahead
of future breakage by migrating "internal" use (i.e. leaving alone the
places where the `base::StringPiece` name is coming from an upstream
method that we override).

Xref: https://bugs.chromium.org/p/chromium/issues/detail?id=691162

Xref: 4294483

Xref: https://docs.google.com/document/d/1d4RnD1uAE2t4iANR0nXy82ASIPGsPuw2mpO6v6T7JKs

shell/browser/usb/electron_usb_delegate.cc

@@ -4,6 +4,7 @@
 
 #include "shell/browser/usb/electron_usb_delegate.h"
 
+#include <string_view>
 #include <utility>
 
 #include "base/containers/contains.h"
@@ -45,7 +46,7 @@ electron::UsbChooserContext* GetChooserContext(
 // These extensions can claim the smart card USB class and automatically gain
 // permissions for devices that have an interface with this class.
 constexpr auto kSmartCardPrivilegedExtensionIds =
-    base::MakeFixedFlatSet<base::StringPiece>({
+    base::MakeFixedFlatSet<std::string_view>({
         // Smart Card Connector Extension and its Beta version, see
         // crbug.com/1233881.
         "khpfeaanjngmcnplbdlpegiifgpfgdco",