Enable idiomatic `record.pt` syntax

[Moelf]

For Record and RecordArray and SlotRecord etc., currently we have code like this:

AwkwardArray.jl/src/all_implementations.jl

Lines 2097 to 2100 in 6ba1c4a

	Base.getindex(
	layout::Record{FIELDS,CONTENTS},
	f::Symbol,
	) where {FIELDS,CONTENTS<:Base.Tuple{Vararg{Content}}} = layout.array.contents[f][layout.at]

This is blocking usage such as cms_events[1].pt, to unblock it, this can be re-written into:

Base.getindex(layout::Record, f::Symbol)  = getfield(layout, :array).contents[f][getfield(layout, :at)]

Base.getproperty(layout::Record, f::Symbol) = layout[f]

of course we don't have to manually do getfield() if we can come up with an internal API for this.