uefi(data-types): allow is_ascii function on Char16 and CStr16

Offers a way to know if a certain UTF-16 string contains only ASCII characters.

uefi/src/data_types/chars.rs

@@ -83,6 +83,12 @@ impl Char16 {
     pub const unsafe fn from_u16_unchecked(val: u16) -> Self {
         Self(val)
     }
+
+    /// Checks if the value is within the ASCII range.
+    #[must_use]
+    pub const fn is_ascii(&self) -> bool {
+        self.0 <= 127
+    }
 }
 
 impl TryFrom<char> for Char16 {

uefi/src/data_types/strs.rs

@@ -415,6 +415,12 @@ impl CStr16 {
         self.0.len() * 2
     }
 
+    /// Checks if all characters in this string are within the ASCII range.
+    #[must_use]
+    pub fn is_ascii(&self) -> bool {
+        self.0.iter().all(|c| c.is_ascii())
+    }
+
     /// Writes each [`Char16`] as a [`char`] (4 bytes long in Rust language) into the buffer.
     /// It is up to the implementer of [`core::fmt::Write`] to convert the char to a string
     /// with proper encoding/charset. For example, in the case of [`alloc::string::String`]