AutoDevInput Text improvement

[phodal]

In current design, AutoDev input will be complex:

• (done) import $ to use variable of context
  • $selction
  • $beforeCursor
• (will) import @ to use build in command and agent
  • @file:/foo/bar/Foo.kt
  • @Rev:<commit_hash>
  • @agent:<agent_id>
  • @symbol:com.example.Foo
  • @msg:<msg_uuid> ?? https://youtrack.jetbrains.com/issue/LLM-2276/chat-input-Message-references
• (will) import / to support some custom command
  • /refactor this
• (will) import # to like to issue or story id
  • #system_id:51
  • #system_id:52
• ....

For example:

Which will make input box complex, in order to use SyntaxHighlighterBase, CompletionContributor or other features, we can design it as a language, which is same to JetBrains' design.

[phodal]

REFS: https://youtrack.jetbrains.com/issue/LLM-2223

Current situation
Only plaintext and code fences are supported.

Desired situation
Settle on a syntax for references. The first syntaxes that come to my mind are:

• `Foo`
• [Foo]
• @foo
• #Foo