Add zend_test.observer.enabled=0 to opcache tests asserting specific TMP count

Necessary to succeed when tests are run with zend_test.observer.enabled=1.

Close PHP tags in tests

Closes GH-12422

Fix DCE of FREE of COALESCE

When encountering the following SSA graph:

BB1:
#2.T1 [string] = COALESCE #1.CV0($str) [null, string] BB2

BB2:
#5.T1 [st

Fix DCE of FREE of COALESCE

When encountering the following SSA graph:

BB1:
#2.T1 [string] = COALESCE #1.CV0($str) [null, string] BB2

BB2:
#5.T1 [string] = QM_ASSIGN string("")

BB3:
#7.X1 [string] = Phi(#2.X1 [string], #5.X1 [string])
FREE #7.T1 [string]

We would currently determine that #7, #5 are dead, and eliminate
the FREE and QM_ASSIGN. However, we cannot eliminate #2, as
COALESCE is also responsible for control flow.

Fix this my marking all non-CV phis as live to start with. This
can be relaxed to check the kind of the source instruction, but
I couldn't immediately come up with a case where it would be
useful.

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Migrate skip checks to --EXTENSIONS--, p3

For rationale, see #6787

Extensions migrated in part 3:
* ftp
* gmp
* iconv
* opcache
* shmop

Clean up remaining opcodes for foreach([] as $x)

Previously, two useless FE_RESET_R and FE_FREE would be left over whether the empty array
was from a literal, a variable, or a class cons

Clean up remaining opcodes for foreach([] as $x)

Previously, two useless FE_RESET_R and FE_FREE would be left over whether the empty array
was from a literal, a variable, or a class constant.

This doesn't pick up the RESET_RW case due to a weakness in our "may throw"
modeling. (for foreach by reference).

Co-Authored-By: Nikita Popov <nikita.ppv@gmail.com>
using https://gist.github.com/nikic/58d367ad605e10299f5433d2d83a0b5b

Closes GH-4949

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