Shadowing default echo with an alias/function can break autosuggestions #843

Describe the bug

If the shell builtin "echo" is shadowed by an alias or a function, it is the alias/function that will be used by zsh-autosuggestions, which can break the autosuggestion by either printing a wrong suggestion, or executing an unwanted function.

To Reproduce

Steps to reproduce the behavior:

git clone https://github.com/zsh-users/zsh-autosuggestions ~/.zsh/zsh-autosuggestions
zsh -df
source ~/.zsh/zsh-autosuggestions/zsh-autosuggestions.zsh

# example of printing the wrong suggestion
alias echo="builtin echo 'DEBUG: '"

# example of executing unwanted function
alias echo="ls; builtin echo 'DEBUG: '"

Expected behavior

I feel like zsh autosuggestions should always use the builtin echo, an being able to change the echo command is not a feature that could be beneficial.

Especially in src/async.zsh, the following "echo"s are vulnerable:

# Fork a process to fetch a suggestion and open a pipe to read from it
	builtin exec {_ZSH_AUTOSUGGEST_ASYNC_FD}< <(
		# Tell parent process our pid
		echo $sysparams[pid]

		# Fetch and print the suggestion
		local suggestion
		_zsh_autosuggest_fetch_suggestion "$1"
		echo -nE "$suggestion"
	)

Screenshots

In the second screenshot, I believe the number 29970 comes from echo $sysparams[pid].

Desktop

• OS + distribution: MacOS Sequoia
• Zsh version: 5.9
• Plugin version: 85919cd (latest tag is v0.7.1)