Glob a/ matches the text a: U+E000 already in the text is read as a masked path separator #194

What's wrong

Before calling DotNet.Glob, glob matching replaces / and \ with the private-use character U+E000, in both the pattern and the text (TextFilter/TextFilter.cs:441-450, MaskedPathSeparator / MaskPathSeparators / IsGlobMatch). The masking never escapes a U+E000 that the text already contains. That character then looks exactly like a masked separator:

• IsMatch("a", "a/") (glob) returns true. Expected: false.
• By the same mechanism, */* and **/ treat U+E000 as a separator, and an exclusion like -*/* hides items whose only "slash" is U+E000.

I checked the first case with a scratch MSTest against main at 5f420d9.

Why it matters

U+E000 is the first private-use code point, and icon fonts really use it (Nerd Fonts' Pomicons, for example, start at E000). ImGui-style UIs, which this library's filters serve, often embed icon glyphs in item labels. A label with such a glyph then matches or fails path-shaped globs depending on whether it has an icon.

Suggested fix

Make the mask unambiguous. Before masking, map any U+E000 already present in the pattern or text to a second private-use character that nothing else uses, so it only ever matches itself. Another way is to escape it in the pattern and substitute it in the text.

Open #175 ("Mask / and \ to different characters") changes the same function, so the two fixes could land together. Note that #175 is about / vs \, not about this aliasing.

Acceptance criteria

• IsMatch("a", "a/") is false, and IsMatch("a", "a") is still true
• Existing / and \ glob tests still pass