Use `binary` property on the file object

What does this MR do?

!68643 (merged) merged earlier last week didn't actually fix the problem. I actually added support the opposite case where you load a text file and its actually binary. 😅

We need to support loading supposed binary files if they are actually text. This MR does fix the problem now.

---

Backend sends a binary property as false for some files that may have a "binary" mime type but are not actually binary. Use that if it is available before determining if a file is binary or text.

How to setup and validate locally (strongly suggested)

1. Open Web IDE for any project.
2. Edit a file. Add an emoji or a non-ASCII somewhere.
3. Rename file to .tex.
4. Commit to any branch.
5. Reopen Web IDE in that branch and try to open .tex file.
6. You will see an indication to download the file, which is not correct.

Expected output after this MR:

• Even though the extension is now .tex (identified as a binary mime type), the contents are still plain text, only the extension was changed. So now the file is editable in the Web IDE.

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.

Security

Does this MR contain changes to processing or storing of credentials or tokens, authorization and authentication methods or other items described in the security review guidelines? If not, then delete this Security section.

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Related to #288006 (closed)