fix: don't change PHP functions which are reserved words

[bshaffer]

with the exception of __halt_compiler, which is so unlikely to be generated as a function name that we don't need to write a case for it, none of the PHP keywords are invalid as class function names. We can safely remove wrapping them.

[codecov]

Codecov Report

Merging #3317 (586dcde) into master (0456289) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##             master    #3317   +/-   ##
=========================================
  Coverage     87.14%   87.14%           
- Complexity     6120     6121    +1     
=========================================
  Files           495      495           
  Lines         24172    24172           
  Branches       2637     2637           
=========================================
+ Hits          21064    21065    +1     
  Misses         2242     2242           
+ Partials        866      865    -1     

Impacted Files	Coverage Δ	Complexity Δ
.../google/api/codegen/util/php/PhpNameFormatter.java	77.27% <100.00%> (ø)	14.00 <3.00> (ø)
.../java/com/google/api/codegen/discovery/Schema.java	84.84% <0.00%> (+0.50%)	43.00% <0.00%> (+1.00%)

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[vam-google]

Can it result in a breaking change for the existing PHP gapic clients which already have the function names changed even though it was not necessary.

[vam-google]

@bshaffer LGTM with a question

[bshaffer]

@vam-google I searched for the function prefix _( in google-cloud-php and there were no results. I believe this is sufficient to ascertain there are no conflicts!

[vchudnov-g]

lgtm, but I'm no PHP expert

[bshaffer]

@jdpedrie caught that this is only the case for PHP 7.0+

Versions of PHP 5.6 and below will throw fatal errors for functions named with reserved words

[bshaffer]

Note: Removing the escaping of functions for PHP Reserved Words for all GAPICs exposes the very low-likelyhood that we might generating a GAPIC with a PHP Fatal Error on PHP < 7 between now and when we deprecate support for PHP < 7.

The plan is to deprecate support in early 2021. If such a fatal error occurs, we will be able to wrap the functions in reserved words for all but DIREGAPIC client libraries, which will all require PHP > 7 from the start.