Ktav editor support 0.6.0 — VS Code + JetBrains + LSP

Tracks ktav Rust crate 0.6.0 and ktav-lang/spec 0.6.0. The
version is realigned to move in lockstep with the format/core (the
previous editor release was 0.3.1). The spec change is key
escaping: keys now process the § 3.7 escape set and add \. (a
literal dot that does not split a dotted path) and \: (a literal
colon that is not a pair separator); a literal backslash in a key is
now written \\. Editor support is updated end-to-end so highlighting,
tokens and diagnostics treat escaped key bytes correctly.

LSP server (ktav-lsp)

• Semantic tokens, document symbols and diagnostics are now
  escape-aware: the pair separator is the first unescaped : / ::
  and dotted-path splitting happens only on unescaped .. So
  a\.b: v is the single key a.b, and a\:: v is the key a: with
  value v.
• Depends on ktav 0.6.0.

IntelliJ plugin

• KtavLexer lexes escaped key segments (\\ \. \: \, \} \] \{ \[ \n \r),
  so a key containing an escaped dot or colon highlights as one key.

TextMate grammar (VS Code + shared grammars/)

• The key-segment pattern accepts \-escapes, matching the spec's key
  escape set.