Source bugs fixed

[bradcarman]

Fixed a couple bugs/breaking changes from v2

• Mechanical.Translational Position, Velocity, and Acceleration had all changed the initial position keyword (from s_0 to s__u_start). Turns out the initial position setting is never actually needed because the RealInput connector should always be driven by an absolute value, therefore this keyword is removed.
• Calculating ForwardDiff derivatives with the Blocks.SampledData component was not working. Included ForwardDiff.value() to handle Dual type calls

[codecov]

Codecov Report

Merging #202 (5633908) into main (c7b207d) will not change coverage.
The diff coverage is 23.07%.

@@           Coverage Diff           @@
##             main     #202   +/-   ##
=======================================
  Coverage   55.61%   55.61%           
=======================================
  Files          48       48           
  Lines        1602     1602           
=======================================
  Hits          891      891           
  Misses        711      711           

Files Changed	Coverage Δ
src/Blocks/sources.jl	70.18% <0.00%> (ø)
src/Mechanical/Translational/sources.jl	43.47% <27.27%> (ø)

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