Improve top level objects support

[montyly]

This is a first step towards better handling of top-level objects

• Split declaration.Enum/Structure to EnumContract/EnumToplevel (same for structure)
• Remove the placeholder top level contract
• Update the parsing accordingly

This PR changes the API, so we will need to evaluate the impact of the public/private detectors.

Related: #619, #708.

[lgtm-com]

This pull request introduces 4 alerts and fixes 2 when merging 0a7738d into e52a2ae - view on LGTM.com

new alerts:

• 2 for Unused import
• 2 for Missing call to __init__ during object initialization

fixed alerts:

• 2 for Missing call to __init__ during object initialization

[lgtm-com]

This pull request introduces 2 alerts and fixes 2 when merging c0406c3 into e52a2ae - view on LGTM.com

new alerts:

• 2 for Missing call to __init__ during object initialization

fixed alerts:

• 2 for Missing call to __init__ during object initialization

[lgtm-com]

This pull request introduces 2 alerts and fixes 2 when merging fe50daa into 1c12a13 - view on LGTM.com

new alerts:

• 2 for Missing call to __init__ during object initialization

fixed alerts:

• 2 for Missing call to __init__ during object initialization

[montyly]

Added support for top-level variable and functions

The support for top-level functions is partial. Among other, what is missing:

• Legacy ast support (impact mostly dapp codebases)
• import X as B is not correctly supported if B is used to refer to top level objects. For example, B.function will lead to generate a High level call instead of an internal call at the IR level

[lgtm-com]

This pull request introduces 6 alerts and fixes 3 when merging 330325a into 1c12a13 - view on LGTM.com

new alerts:

• 3 for Unused import
• 2 for Missing call to __init__ during object initialization
• 1 for __eq__ not overridden when adding attributes

fixed alerts:

• 3 for Missing call to __init__ during object initialization

[lgtm-com]

This pull request introduces 3 alerts and fixes 3 when merging d778ed6 into 1c12a13 - view on LGTM.com

new alerts:

• 2 for Missing call to __init__ during object initialization
• 1 for __eq__ not overridden when adding attributes

fixed alerts:

• 3 for Missing call to __init__ during object initialization

[lgtm-com]

This pull request introduces 2 alerts and fixes 3 when merging d1eee22 into 1c12a13 - view on LGTM.com

new alerts:

• 2 for Missing call to __init__ during object initialization

fixed alerts:

• 3 for Missing call to __init__ during object initialization