flatc -M: escape make-special characters in depfiles

[vee1e]

flatc -M writes dependency rules with filenames unescaped. Make treats $, #, :, space, and backslash as syntax, so a schema whose include path contains any of them produces a depfile that make or Ninja parses wrong. For example an include named my schema#1.fbs yields a rule that make splits at the space and truncates at the #.

GCC and Clang already escape these characters in their -M/-MD output, and glslang does the same with its writeEscapedDepString helper. This change matches that behavior.

What it does:

• Adds EscapeMakeDep to util.h/util.cpp, escaping backslash first, then space, #, :, and $ (as $$).
• Applies it to every active GenerateMakeRule implementation: Java/C#, C++, Rust, Dart, binary, text, and TypeScript.
• Emits each rule as one line instead of word-wrapping. Wrapping split escaped filenames on their spaces, undoing the escape.

Brackets are intentionally not escaped: Ninja's depfile parser does not unescape [, so escaping them would corrupt filenames for that consumer.

Adds a unit test covering the five characters, combined input, a trailing backslash, and empty and plain filenames.