fix incorrect docs for add_*_script

They claimed that all of these functions accepted any posargs or varargs
that install scripts supported. This was inconsistent with both the
types that meson currently allowed, and the types that we documented in
refman 1.0 *should* be allowed.

Take the opportuninty to be clear as refman 1.0 never was, about the
difference between types supported in the first posarg, and the ypes
supported in succeeding varargs.

docs/yaml/builtins/meson.yaml

@@ -34,18 +34,17 @@ methods:
 
     posargs:
       script_name:
-        type: str | file | external_program | exe | custom_tgt | custom_idx
+        type: str | file | external_program
         description: |
           The script to execute.
 
-          *(since 0.55.0)* The output of [[configure_file]], [[files]], and [[find_program]]
-          as well as strings are accepted.
+          *(since 0.55.0)* The output of [[find_program]] as well as strings are accepted.
 
           *(since 0.57.0)* [[@file]] objects and the output of [[configure_file]] may be used.
 
     varargs:
       name: arg
-      type: str | file | external_program | exe | custom_tgt | custom_idx
+      type: str | file | external_program
       since: 0.49.0
       description: |
         Additional arguments
@@ -53,8 +52,6 @@ methods:
         *(since 0.55.0)* The output of [[configure_file]], [[files]], and [[find_program]]
         as well as strings are accepted.
 
-        *(since 0.57.0)* [[@file]] objects and the output of [[configure_file]] may be used.
-
   - name: add_install_script
     returns: void
     description: |
@@ -89,8 +86,26 @@ methods:
       shell would. If your script uses Python, `shlex.split()` is the
       easiest correct way to do this.
 
-    posargs_inherit: meson.add_dist_script
-    varargs_inherit: meson.add_dist_script
+    posargs:
+      script_name:
+        type: str | file | external_program | exe | custom_tgt | custom_idx
+        description: |
+          The script to execute.
+
+          *(since 0.55.0)* The output of [[find_program]], [[executable]],
+          [[custom_target]], as well as strings are accepted.
+
+          *(since 0.57.0)* [[@file]] objects and the output of [[configure_file]] may be used.
+
+    varargs:
+      name: arg
+      type: str | file | external_program | exe | custom_tgt | custom_idx
+      since: 0.49.0
+      description: |
+        Additional arguments
+
+        *(since 0.55.0)* The output of [[find_program]], [[executable]],
+        [[custom_target]], as well as strings are accepted.
 
     kwargs:
       skip_if_destdir: