[BUG] "Replace with" also uses regex together with "Find what" in regex mode

Is there an existing issue for this?

• I have searched the existing issues

Description of the Issue

The "Replace with" when replacing text shouldn't use regex.

Steps To Reproduce

Press Ctrl+Shift+F and routinely replace text in a Search Mode "Regular expression":

Text:
abcd

Find what:
ab[c]

Replace with:
ab\)

Current Behavior

ab)d

Expected Behavior

ab\)d

// the "Replace with" shouldn't use regex, it should replace the matched string as a plain text

Debug Information

Notepad++ v8.6.4   (32-bit)
Build time : Feb 20 2024 - 00:11:10
Path : C:\Program Files (x86)\Notepad++\notepad++.exe
Command Line : "C:\REDACTED.xml"
Admin mode : OFF
Local Conf mode : OFF
Cloud Config : OFF
OS Name : Windows 10 Enterprise (64-bit)
OS Version : 22H2
OS Build : 19045.5679
Current ANSI codepage : 1252
Plugins : 
    HexEditor (0.9.12)
    mimeTools (3.1)
    NppConverter (4.6)
    NppExport (0.4)

Anything else?

Note: when adding a closing parenthesis ) at the end of a "Replace with", even though missing an opening parenthesis it makes it invalid, it effectively just silently drops this character. Users will be surprised when (if) double-checking their replacement results that such characters disappeared (whereas Notepad++ doesn't even inform us of the replacement result unless we manually scroll to find it, being error prone). There is no intuitive way to "convert plain text into an equivalent regex" for this purpose either. It's not intuitive, it's not documented, there is no warning about this behavior, and there is no toggle to disable it.

Note: obviously, IDEs like IntelliJ IDEA follow a proper (and logical) implementation of not using regex in the "Replace with", except for things like replacing $1 with the capture group value. Pretty much everyone will be used to this behavior over the course of their life, and when they quickly go use Notepad++ for any reason, they'll introduce severe bugs to any text they convert.

Reproduce the issue through the Ctrl+Shift+F search-and-replace workflow with Regular expression mode enabled, using the example text and patterns in the report. Trace the replacement handling from that entry point and verify that replacement text is treated literally; done when the escaped parenthesis remains in the result as expected.