Add warning when converting global phase operator to OpenQASM 2.0 #14536

Job	Run time
Packaging test	1m 16s
Type check	2m 12s
Changed files test	1m 11s
Doc test	2m 13s
Format check	10s
Isolated pytest Ubuntu	8m 0s
Lint check	2m 49s
Notebook formatting	10s
Check consistency of requirements	26s
Pytest Ubuntu (3.9)	8m 5s
Misc check	5s
Pytest Ubuntu (3.10)	7m 49s
Shell check	6s
Pytest Ubuntu (3.11)	7m 55s
Build protos	9s
Coverage check	19m 32s
Pytest MacOS (3.9)	13m 55s
Notebook Tests against PR	9m 20s
Changed Notebooks Isolated Test against Cirq stable (partition-0)	46s
Pytest MacOS (3.10)	7m 28s
Changed Notebooks Isolated Test against Cirq stable (partition-1)	52s
Pytest MacOS (3.11)	14m 23s
Changed Notebooks Isolated Test against Cirq stable (partition-2)	48s
Bundle file consistency	41s
Changed Notebooks Isolated Test against Cirq stable (partition-3)	49s
Typescript tests coverage	31s
Typescript lint check	32s
Typescript tests	34s
Pytest Windows (3.9)	10m 54s
Pytest Windows (3.10)	10m 36s
Pytest Windows (3.11)	8m 37s
	2h 22m 54s

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