Update csharp-ts-mode font-lock (bug#73369)

Update csharp-ts-mode font-lock (bug#73369)

Adapt to the latest c-sharp grammar.

* lisp/progmodes/csharp-mode.el:
(csharp-ts-mode--test-this-expression):
(csharp-ts-mode--test-interpolated-string-text):
(csharp-ts-mode--test-type-constraint):
(csharp-ts-mode--test-type-of-expression):
(csharp-ts-mode--test-name-equals):
(csharp-ts-mode--test-if-directive):
(csharp-ts-mode--test-method-declaration-type-field): New
functions.
(csharp-ts-mode--type-field): New variable.
(csharp-ts-mode--font-lock-settings): Fix font-lock rules.