[stable10] drop php 7.0 and add phpunit7

[phil-davis]

Description

Combination of
#35774 "Introduce phpstan" (note: has now been merged to stable10)
#35786 "drop PHP 7.0"
#34921 Bump phpunit7 (backport)
Extra commit: "Update method signatures for EncryptionTrait markTestSkipped and assertTrue" to fix a problem reported in the encryption unit test code (which is not in master), to fix:

PHP Fatal error:  Declaration of Test\Traits\EncryptionTrait::markTestSkipped(string $message = '') must be compatible with PHPUnit\Framework\Assert::markTestSkipped(string $message = ''): void in /home/phil/git/owncloud/core/apps/dav/tests/unit/Connector/Sabre/RequestTest/EncryptionUploadTest.php on line 36
PHP Fatal error:  Declaration of Test\Traits\EncryptionTrait::assertTrue($condition, $message = '') must be compatible with PHPUnit\Framework\Assert::assertTrue($condition, string $message = ''): void in /home/phil/git/owncloud/core/apps/dav/tests/unit/Connector/Sabre/RequestTest/EncryptionUploadTest.php on line 36

Related Issue

Motivation and Context

See if it passes all together.

How Has This Been Tested?

CI

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Database schema changes (next release will require increase of minor version instead of patch)
• Breaking change (fix or feature that would cause existing functionality to change)
• Technical debt
• Tests only (no source changes)

Checklist:

• Code changes
• Unit tests added
• Acceptance tests added
• Documentation ticket raised:

[codecov]

Codecov Report

Merging #35789 into stable10 will decrease coverage by 0.12%.
The diff coverage is 75.45%.

@@              Coverage Diff               @@
##             stable10   #35789      +/-   ##
==============================================
- Coverage       64.84%   64.71%   -0.13%     
+ Complexity      20243    19487     -756     
==============================================
  Files            1299     1298       -1     
  Lines           77220    76901     -319     
  Branches         1301     1301              
==============================================
- Hits            50070    49770     -300     
+ Misses          26765    26746      -19     
  Partials          385      385

Flag	Coverage Δ	Complexity Δ
#javascript	53.85% <ø> (ø)	0 <ø> (ø)	⬇️
#phpunit	65.87% <75.45%> (-0.13%)	19487 <23> (-756)

Impacted Files	Coverage Δ	Complexity Δ
core/Command/Upgrade.php	0% <ø> (ø)	29 <0> (-39)	⬇️
lib/private/Session/Session.php	100% <ø> (ø)	5 <0> (ø)	⬇️
lib/private/DB/MigrationService.php	90.37% <ø> (-0.08%)	51 <0> (-2)
lib/private/DB/ConnectionFactory.php	90.27% <ø> (+7.38%)	21 <0> (ø)	⬇️
lib/private/Session/CryptoWrapper.php	47.05% <ø> (ø)	6 <0> (ø)	⬇️
apps/files/lib/Command/TransferOwnership.php	0% <ø> (ø)	40 <0> (-6)	⬇️
apps/dav/lib/CardDAV/SyncService.php	45.45% <ø> (+0.4%)	25 <0> (-2)	⬇️
core/Command/Maintenance/DataFingerprint.php	100% <ø> (ø)	4 <0> (ø)	⬇️
lib/private/Files/Node/Folder.php	96.09% <ø> (-0.09%)	42 <0> (-3)
apps/files/lib/Command/VerifyChecksums.php	91.56% <ø> (-0.2%)	23 <0> (-9)
... and 292 more

---

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[codecov]

Codecov Report

Merging #35789 into stable10 will decrease coverage by 0.37%.
The diff coverage is 70%.

@@              Coverage Diff               @@
##             stable10   #35789      +/-   ##
==============================================
- Coverage       65.09%   64.71%   -0.38%     
+ Complexity      20239    19487     -752     
==============================================
  Files            1300     1298       -2     
  Lines           77238    76901     -337     
  Branches         1301     1301              
==============================================
- Hits            50279    49770     -509     
- Misses          26574    26746     +172     
  Partials          385      385

Flag	Coverage Δ	Complexity Δ
#javascript	53.85% <ø> (ø)	0 <ø> (ø)	⬇️
#phpunit	65.87% <70%> (-0.42%)	19487 <11> (-752)

Impacted Files	Coverage Δ	Complexity Δ
lib/private/DB/ConnectionFactory.php	90.27% <ø> (+7.38%)	21 <0> (ø)	⬇️
index.php	0% <0%> (ø)	0 <0> (ø)	⬇️
console.php	0% <0%> (ø)	0 <0> (ø)	⬇️
lib/private/DB/MySqlTools.php	88.46% <82.35%> (+88.46%)	11 <11> (+7)	⬆️
lib/private/DB/OCPostgreSqlPlatform.php	24.13% <0%> (-72.42%)	15% <0%> (ø)
...aring/appinfo/Migrations/Version20190410160725.php	75% <0%> (-25%)	4% <0%> (+2%)
core/Application.php	25.47% <0%> (-13.76%)	1% <0%> (-24%)
apps/files/lib/AppInfo/Application.php	30.55% <0%> (-9.93%)	1% <0%> (-6%)
settings/Application.php	51.44% <0%> (-8.75%)	2% <0%> (-39%)
...e/AppFramework/DependencyInjection/DIContainer.php	64.84% <0%> (-8.05%)	15% <0%> (-66%)
... and 198 more

---

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Δ = absolute <relative> (impact), ø = not affected, ? = missing data
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[phil-davis]

CI green - great stuff.
This is a working example of phpstan, dropping PHP 7.0 and bumping PHPunit from 6 to 7 on stable10

[phil-davis]

Later version is #35804