Fix Emacs 26.3 compatibility issues

* eglot.el (eglot--semtok-after-send-changes): Use cl-getf instead
of plist-get for setf.

* eglot-tests.el (eglot--tests-connect): Use split-string instead
of string-split.
(eglot-test-rust-completion-exit-function): Replace skip-when with
skip-unless.
(eglot-test-semtok-basic, eglot-test-semtok-refontify): Skip if
text-property-search-forward unavailable.

Author: joaotavora

eglot-tests.el

@@ -299,7 +299,7 @@ directory hierarchy."
          (eglot-sync-connect t)
          (eglot-connect-timeout timeout)
          (eglot-server-programs
-          (if server `((,major-mode . ,(string-split server)))
+          (if server `((,major-mode . ,(split-string server)))
             eglot-server-programs)))
     (apply #'eglot--connect (eglot--guess-contact))))
 
@@ -775,7 +775,7 @@ directory hierarchy."
   ;; This originally appeared in github#1339
   (skip-unless (executable-find "rust-analyzer"))
   (skip-unless (executable-find "cargo"))
-  (skip-when (getenv "EMACS_EMBA_CI"))
+  (skip-unless (not (getenv "EMACS_EMBA_CI")))
   (eglot--with-fixture
       '(("cmpl-project" .
          (("main.rs" .
@@ -1583,6 +1583,7 @@ GUESSED-MAJOR-MODES-SYM are bound to the useful return values of
 (ert-deftest eglot-test-semtok-basic ()
   "Test basic semantic tokens fontification."
   (skip-unless (executable-find "clangd"))
+  (skip-unless (fboundp 'text-property-search-forward))
   (eglot--with-fixture
       `(("project" . (("main.c" . "int main() { int x = 42; return x; }"))))
     (with-current-buffer
@@ -1602,6 +1603,7 @@ GUESSED-MAJOR-MODES-SYM are bound to the useful return values of
 (ert-deftest eglot-test-semtok-refontify ()
   "Test semantic tokens refontification after edits."
   (skip-unless (executable-find "clangd"))
+  (skip-unless (fboundp 'text-property-search-forward))
   (eglot--with-fixture
       `(("project" . (("code.c" . "int foo() { return 0; }"))))
     (with-current-buffer

eglot.el

@@ -5017,7 +5017,7 @@ See `eglot--semtok-request' implementation for details.")
 
 (defun eglot--semtok-after-send-changes ()
   ;; (trace-values "Dispatching")
-  (setf (plist-get eglot--semtok-state :dispatched) t))
+  (setf (cl-getf eglot--semtok-state :dispatched) t))
 
 (cl-defun eglot--semtok-request (beg end &aux (docver eglot--docver))
   "Ask for tokens.  Arrange for BEG..END to be font-lock flushed."