Improve Lepcha composition rules and rename its native name

* lisp/language/indian.el ("Lepcha"): Rename lepcha script
native name and improve composition rules.  (Bug#55869)

* etc/HELLO: Rename Lepcha script native name.

etc/HELLO

@@ -76,7 +76,7 @@ Kharoṣṭhī (𐨑𐨪𐨆𐨛𐨁)	𐨣𐨨𐨲𐨪𐨆 𐨐𐨪𐨅𐨨𐨁
 Khmer (ភាសាខ្មែរ)	ជំរាបសួរ
 Lakota (Lakȟotiyapi)	Taŋyáŋ yahí!
 Lao (ພາສາລາວ)	ສະບາຍດີ / ຂໍໃຫ້ໂຊກດີ
-Lepcha (ᰛᰩᰵ)	ᰂᰦᰕᰥᰬ
+Lepcha (ᰛᰩᰵᰛᰧᰵᰶ)	ᰂᰦᰕᰥᰬ
 Limbu (ᤕᤰᤌᤢᤱ ᤐᤠᤴ)	ᤛᤣᤘᤠᤖᤥ
 Makasar (𑻪𑻢𑻪𑻢)	𑻦𑻤𑻵𑻱
 Malayalam (മലയാളം)	നമസ്കാരം

lisp/language/indian.el

@@ -249,7 +249,7 @@ Grantha script, are supported in this language environment."))
             (coding-system utf-8)
             (coding-priority utf-8)
             (input-method . "lepcha")
-            (sample-text . "Lepcha (ᰛᰩᰵ)	ᰂᰦᰕᰥᰬ")
+            (sample-text . "Lepcha (ᰛᰩᰵᰛᰧᰵᰶ)	ᰂᰦᰕᰥᰬ")
             (documentation . "\
 Lepcha language and its script are supported in this
 language environment."))
@@ -756,7 +756,8 @@ language environment."))
                         (list (vector
                                ;; Consonant based syllables
                                (concat consonant other-signs "?" vowel "?"
-                                       consonant-sign "?" subjoined-letter "?")
+                                       consonant-sign "?" subjoined-letter "?"
+                                       other-signs "?")
                                1 'font-shape-gstring))))
 
 (provide 'indian)