Closes #39036 

The open path prompt will now show hidden files when "." is entered.
Also fixes an issue with "open this directory" showing twice when used
by the "toolchain: add toolchain" prompt.

With a tree of 
```
zed-industries
├── .hidden
├── .hidden-file
├── zed
├── zed-working
├── zeta
└── zeta-dataset
```
**Before:**
<img width="656" height="174" alt="image"
src="https://github.com/user-attachments/assets/abf30ce3-b1c2-4a14-a45d-c17b6c3aef6f"
/>

**After (current directory view without inputting "."):**
<img width="648" height="261" alt="image"
src="https://github.com/user-attachments/assets/00c65546-32c1-4c85-a05c-53152ab2f942"
/>

**After (when inputting "." to see hidden entries):**
<img width="618" height="156" alt="image"
src="https://github.com/user-attachments/assets/8453ae89-b1a7-44d4-9f7d-ed89e55a7020"
/>


Release Notes:
- Made Zed's built in file picker to show all hidden files by default