[receiver/windowsperfcountersreceiver] Emit double values instead of integer values

[BinaryFissionGames]

Description:

• Emit the scraped float64 values instead of truncating to int64
• Removed now unused function for initializing the datapoint as double

Link to tracking Issue: #9136

Testing:
Updated unit test to expect double value
Manually tested with this config:

receivers:
  windowsperfcounters:
    collection_interval: 10s
    metrics:
      processor.time:
        description: active and idle time of the processor
        unit: "%"
        gauge:
    perfcounters:
    - object: "Processor Information"
      instances: "*"
      counters:
        - name: "% Processor Time"
          metric: processor.time

exporters:
  logging:
    loglevel: debug

service:
  pipelines:
    metrics:
      receivers: [windowsperfcounters]
      exporters: [logging]

I see datapoints with double values:

NumberDataPoints #4
Data point attributes:
     -> instance: STRING(0,_Total)
StartTimestamp: 1970-01-01 00:00:00 +0000 UTC
Timestamp: 2022-04-11 16:41:18.6038037 +0000 UTC
Value: 0.866840

[djaglowski]

Flaky unit test keeps failing, but this LGTM.