[ShellScript] Tweak command reference scopes and symbols

This commit...

1. introduces a common `meta.command` scope applied to function calls and
   function name references.
2. adjusts reference definitions accordingly.

Goal is a common and unique scope to target function or command references.

ShellScript/Bash.sublime-syntax

@@ -328,7 +328,7 @@ contexts:
  - alias-name-chars
 
  alias-name-chars:
- - meta_scope: meta.variable.shell entity.name.function.shell
+ - meta_scope: meta.command.shell entity.name.function.shell
  - include: line-continuations
  - include: literal-unquoted-content
  - match: '{{opt_break}}'
@@ -857,10 +857,10 @@ contexts:
  cmd-builtin:
  # cmd modifier commands are directly followed by simple commands
  - match: '{{modifier_cmds}}'
- scope: meta.function-call.identifier.shell meta.path.shell support.function.shell
+ scope: meta.function-call.identifier.shell meta.command.shell support.function.shell
  # shell built-in commands with arbritary arguments
  - match: '{{builtin_cmds}}'
- scope: meta.function-call.identifier.shell meta.path.shell support.function.shell
+ scope: meta.function-call.identifier.shell meta.command.shell support.function.shell
  push:
  - cmd-args-meta
  - cmd-args
@@ -890,7 +890,7 @@ contexts:
  - path-pattern-begin
 
  cmd-name-body:
- - meta_scope: meta.function-call.identifier.shell meta.path.shell variable.function.shell
+ - meta_scope: meta.function-call.identifier.shell meta.command.shell variable.function.shell
  - include: line-continuations
  - include: path-pattern-content
  - match: '{{cmd_break}}'
@@ -984,7 +984,7 @@ contexts:
  push: function-declaration-name-chars
 
  function-declaration-name-chars:
- - meta_scope: meta.variable.shell entity.name.function.shell
+ - meta_scope: meta.command.shell entity.name.function.shell
  - include: line-continuations
  - include: literal-unquoted-content
  - match: '{{word_break}}'
@@ -1003,7 +1003,7 @@ contexts:
  push: function-reference-name-chars
 
  function-reference-name-chars:
- - meta_scope: meta.variable.shell variable.function.shell
+ - meta_scope: meta.command.shell variable.function.shell
  - include: line-continuations
  - include: literal-unquoted-content
  - match: '{{word_break}}'
@@ -1462,7 +1462,7 @@ contexts:
  - path-pattern-begin
 
  unquoted-statements-word-body:
- - meta_scope: meta.string.shell meta.path.shell variable.function.shell
+ - meta_scope: meta.string.shell meta.command.shell variable.function.shell
  - include: line-continuations
  - include: path-pattern-content
  - match: '{{cmd_break}}'