feat: language support for mail files (#12945)

runtime/queries/mail/highlights.scm

@@ -0,0 +1,28 @@
+; header fields
+[
+  (header_field_email)
+  (header_field_subject)
+  (header_field)
+] @keyword
+
+; delimited punctuation
+(header_separator) @punctuation.delimiter
+(email_delimiter) @punctuation.delimiter
+
+; email subject contents
+(header_subject
+  (subject) @markup.bold)
+; extra metadata headers
+(header_other
+  (header_unstructured) @comment)
+
+; Addressee Name (Firstname, Lastname, etc.)
+(atom) @variable
+
+; Email Address
+(email) @string
+
+; Quoted Reply
+(quote_marker) @punctuation.special
+(quote_contents) @markup.quote
+

runtime/queries/mail/textobjects.scm

@@ -0,0 +1,13 @@
+(atom_block
+  (atom) @entry.inside) @entry.around
+
+(email_address) @entry.around
+(header_other
+  (header_unstructured) @entry.around)
+
+(quoted_block)+ @comment.around
+
+(body_block)+ @function.around
+
+(header_subject
+  (subject) @function.around)