Support convert Should -HaveCount to v6 syntax

[johlju]

Dependent on issue being tracked in pester/Pester#2534.

[johlju]

There will be a parameter Count for Should-BeCollection. But it while it being developed ww can use .Count instead and use Should-Be.

pester/Pester#2534 (comment)

The Pester 5 syntax:

$collection | Should -HaveCount 3
# or
$collection | Get-Something | Should -HaveCount 3

Would be converted to:

($collection).Count | Should-Be 3
# or
($collection | Get-Something).Count | Should-Be 3

[johlju]

When Count is introduced to Should-BeCollection then the above Pester 5 syntax should be converted to:

$collection | Should-BeCollection -Count 3
# or
$collection | Get-Something | Should-BeCollection -Count 3

[johlju]

It might be worth waiting for Count to be introduced to Should-BeCollection because it would be a pain to convert it back if it has first been converted to .Count.