Simplify the reading of DictionaryProperty

[Numpsy]

A thought whilst we're open for API changes:

As it stands, for each entry in the property name dictionary, DictionaryProperty

• creates a new instance of DictionaryEntry
• calls the Read function, which stores the bytes for the entry
• reads the Name property, which decodes the stored bytes and returns the string
• discards the DictionaryEntry

This seems a bit round about to me for what it's doing, so I propose just doing a simple inline read and not having an instanced DictionaryEntry class.

This also makes it easier to see if the ReadBytes calls could be changed to Read or merged together and and then sliced with spans later.

[Numpsy]

TBD: I'm not sure if this needs to be public at all

[jeremy-visionaid]

OLE isn't really my thing, so I have no idea how this intended to be used. I'm generally in favour of sealing unless there's a reason not to and the class is designed to be extended though. I'm happy to defer to your judgement. The rest all LGTM.

[Numpsy]

Basically I'm not clear why DictionaryProperty would be public when all the other implementations of IProperty (i.e the TypedPropertyValue classes) appear to be internal.

Usage of those classes is generally part of PropertyFactory and/or PropertySetStream, and both of those are internal

[Numpsy]

Has a trivial reduction in allocations as a side effect
For example, from

| Method                  | Job      | Runtime  | Mean     | Error    | StdDev   | Gen0   | Gen1   | Allocated |
|------------------------ |--------- |--------- |---------:|---------:|---------:|-------:|-------:|----------:|
| CreateCompoundDocument  | .NET 6.0 | .NET 6.0 | 35.37 us | 0.605 us | 0.536 us | 1.0986 |      - |   6.95 KB |
| ReadDocFile             | .NET 6.0 | .NET 6.0 | 92.09 us | 1.808 us | 3.167 us | 7.0801 | 0.2441 |  43.85 KB |
| ReadOnePropFromADocFile | .NET 6.0 | .NET 6.0 | 88.74 us | 1.363 us | 1.208 us | 6.7139 | 0.1221 |  41.45 KB |
| CreateCompoundDocument  | .NET 8.0 | .NET 8.0 | 31.27 us | 0.596 us | 0.557 us | 1.0986 |      - |   6.93 KB |
| ReadDocFile             | .NET 8.0 | .NET 8.0 | 77.86 us | 1.545 us | 2.581 us | 6.8359 |      - |  43.43 KB |
| ReadOnePropFromADocFile | .NET 8.0 | .NET 8.0 | 79.34 us | 1.586 us | 4.446 us | 6.3477 |      - |  41.22 KB |

to

| Method                  | Job      | Runtime  | Mean     | Error    | StdDev   | Median   | Gen0   | Gen1   | Allocated |
|------------------------ |--------- |--------- |---------:|---------:|---------:|---------:|-------:|-------:|----------:|
| CreateCompoundDocument  | .NET 6.0 | .NET 6.0 | 35.73 us | 0.645 us | 1.130 us | 35.55 us | 1.0986 |      - |   6.95 KB |
| ReadDocFile             | .NET 6.0 | .NET 6.0 | 92.24 us | 1.713 us | 3.500 us | 90.89 us | 7.0801 | 0.2441 |  43.73 KB |
| ReadOnePropFromADocFile | .NET 6.0 | .NET 6.0 | 88.32 us | 0.852 us | 0.711 us | 88.24 us | 6.7139 | 0.2441 |  41.33 KB |
| CreateCompoundDocument  | .NET 8.0 | .NET 8.0 | 32.40 us | 0.621 us | 1.557 us | 31.94 us | 1.0986 |      - |   6.93 KB |
| ReadDocFile             | .NET 8.0 | .NET 8.0 | 77.68 us | 1.383 us | 1.593 us | 77.75 us | 6.8359 |      - |  43.31 KB |
| ReadOnePropFromADocFile | .NET 8.0 | .NET 8.0 | 76.61 us | 1.385 us | 1.228 us | 76.68 us | 6.3477 |      - |   41.1 KB |

(that will vary depending on how many properties there are)