Add KQL as a text container language, highlighted and formatted

[marcosqlbi]

Closes #101.

Kusto Query Language joins DAX and SQL Server: a text container can be KQL, the
title-bar chip offers it, F6 formats it, and .kql files and kql / kusto
fences import as KQL.

Why this shape

SQLBI.Whiteboard.Kql wraps Microsoft.Azure.Kusto.Language the way
SQLBI.Whiteboard.SqlServer wraps ScriptDOM. Microsoft ships the parser, the
classifier, and the formatter for their own language, so unlike DAX there is no
grammar to write here and nothing to keep current by hand as KQL grows. The
package is Apache-2.0, has no dependencies of its own, and targets
netstandard2.0.

Only the syntax is judged. A board carries a snippet rather than a connection,
so the semantic pass reports every table and column it cannot resolve; all of
those would be false alarms on a whiteboard, so acceptance and the F6 guard both
read syntax diagnostics alone.

The one place the library default was overridden

Formatting keeps the author's spacing around the assignment sign. The library
default writes join kind = inner hint.strategy = broadcast, which rewrites the
hints that real queries carry; the examples on the issue are all written the
tight way. Everything else is the library's own layout.

As with DAX and SQL, formatting compares the tokens and the comments before and
after and returns the text untouched when they differ, so F6 can never quietly
change a query.

Notes for review

• The language is appended last everywhere, so a board or a settings file saved
  before this release keeps its Snippet format order and simply gains KQL at the
  end. There is a test for that.
• A bare word is a valid KQL query, so KQL would claim Agenda if it were tried
  before Plain text. Plain text stays first by default and always accepts, so
  this only reaches someone who has reordered the list deliberately.
• SQLBI.Whiteboard.Kql.dll is in the pipeline signing list. The installer
  harvests the publish folder, so it and Kusto.Language.dll need nothing there.
• Verified in the running application, not only in tests: both containers of a
  .wimport imported as KQL, highlighted, and F6 reformatted a one-line query
  in place while keeping T=7d and kind=inner as written.

dotnet build Whiteboard.sln -c Release is clean with no warnings, and the
smoke tests pass.

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